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FUEL AND REFRACTORY 
MATERIALS 



FUEL AND REFRACTORY 
MATERIALS 



BY 



A. HUMBOLDT SEXTON 

F.I.C., F.C.S. * 

Past President of the West of Scotland Iron and Steel Institute 



NEW EDITION 

COMPLETELY REVISED AND ENLARGED 

BY 

W. B. DAVIDSON 

D.Sc, Ph.D., F.I.C. 



NEW YORK 

D. VAN NOSTRAND COMPANY 

EIGHT WARREN STREET 

1921 






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I 

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PEEFACE 

This book is a revised edition of Professor Sexton's well- 
known work on " Fuel and Refractory Materials." 

In revising the book it has not been found necessary 
to make drastic alterations in the original text. 

Slight inconsistencies in statistics and figures have been 
as far as possible eliminated, but it has not been considered 
advisable to adopt either the Centigrade or the Fahrenheit 
scale in thermometry to the exclusion of the other. 

The quite recent new views as to the constitution of 
coal have not been incorporated, as it is felt the subject is 
still in its infancy ; the same remark applies to some modern 
theories of the chemistry of coking. 

The chapters on Liquid and Gaseous Fuels have been 
considerably modified and enlarged. Chapter VIII. on 
" Recovery of By-products " has been almost entirely 
rewritten, and is now entitled " By-products and Low- 
temperature Carbonization . ' ' 

The Chapters on " Testing Fuels " and " Refractory 
Materials " have been brought up to date and enlarged. 

Some of the old illustrations have been discarded and a 
few new ones introduced. 

A Spanish translation by Senor C. de Madariaga, of 

Madrid, is in preparation. 

W. B. D. 



CONTENTS 

'CHAP. 

I. Combustion 
II. Heating Power of Fuels 

III. Fuels — Wood, Peat, Coal 

IV. Solid Prepared Fuels — Charcoal, Peat-charcoal, Coke 

V. COAL-WASHING 

VI. Liquid Fuels 
VII. Gaseous Fuel 
Till. By-products and Low-temperature Carbonization 
IX. Furnaces for Metallurgical Purposes 
X. Supply of Air to the Furnace — Removal of Waste 

Products — Smoke — Prevention of Smoke 
XL Pyrometry .... 

XII. Calorimetry .... 

XIII. Utilization of Fuel 

XIV. Testing Fuels .... 
XV. Refractory Materials — Bricks — Crucibles 

Notes and Tables 
Index ... 



1 

26 

41 

73 

118 

126 

138 

193 

212 

261 
268 
297 
315 
322 
329 
365 
369 



FUEL 

AND REFRACTORY MATERIALS 

CHAPTER I 

COMBUSTION 

Combustion. — Heat is required in almost all metal- 
lurgical operations, and is always obtained directly or in- 
directly by the combustion of substances called fuels. A 
consideration of the phenomena of combustion and of the 
nature and methods of using fuel is therefore essential as an 
introduction to the study of metallurgy. 

Chemical combination is almost invariably attended with 
the evolution of heat, and when this is sufficient to raise the 
combining bodies or the products of combination to the tem- 
perature at which they evolve light, combustion is said to 
take place. Combustion may therefore be defined as vigorous 
chemical combination, attended with the evolution of light. 

In practice the combination is always between a com- 
bustible or fuel and the oxygen of the air, which is therefore 
said to support combustion. 

Conditions which favour Combustion. — In order that 
combustion may begin, the fuel must be brought in contact 
with the air at a suitable temperature ; and in order that it 
may continue, this temperature must be kept up, a supply of 
oxygen must be maintained, and the products of combustion 
must be removed. 

As a rule, the larger the surface of the combustible in 
contact with the air, the more readily will combustion take 

(D107) 1 B 



2 FUEL 

place, and as gases, by the mobility of their molecules, allow 
of the largest possible amount of contact, they, if combustible, 
usually burn very readily. 

If a combustible gas be allowed to escape from a tube into 
the air at a temperature at which it will burn, combustion 
takes place with great facility ; for as the gas comes into the 
air diffusion takes place, the gas molecules are brought into 
close contact with the oxygen molecules, and they combine, 
forming a zone of combustion surrounding a core of gas, and 
thus producing a flame. 

If a combustible gas be thoroughly mixed with air and a 
light be applied, combustion takes place almost instantly 
through the whole mass, travelling very rapidly from particle 
to particle ; heat is suddenly evolved, great expansion results, 
and an explosion of more or less violence takes place. 

Liquids do not burn readily in mass, for the air cannot 
penetrate them, and there is therefore only contact at the, 
comparatively small, surface of the liquid. There are 
apparent exceptions to this, due to the fact that most 
liquids are volatile, and combination therefore takes place 
near the liquid surface, between the vapour and the air. 
If a combustible liquid be broken up into a fine spray by 
a steam or air jet, it will burn almost exactly as if it were 
a gas, and will form an explosive mixture with air. 

Combustible solids usually burn readily when in pieces of 
such a size as to allow ready access of air, and at the same 
time exposing a large surface of contact. If the lumps be too 
large the contact surface is too small and combustion is 
hindered, and if the substance be in a powder the air will be 
unable to penetrate, and therefore there will still only be a 
small surface of contact. If a finely -powdered solid fuel be 
projected at a high temperature into air, it burns very rapidly, 
almost exactly in the same way as a gas, and such a powder 
may even form an explosive mixture with air. It is quite 
certain that many colliery and other explosions, if not entirely 
due to, are at any rate very much intensified by the presence 
of coal or other combustible dust in the air. 



COMBUSTION 3 

Many examples of the influence of contact surface are 
familiar. A piece of charcoal of large size will burn readily, 
because being very porous air can find its way into it, and 
thus provide a large contact surface, while a large lump of 
anthracite, not being porous, will hardly burn at all. Paper 
and wood-shavings are employed to light a fire, though they 
have almost the same composition as the wood, because, 
owing to their thinness, they expose a large surface to the 
air, and ignite readily. These and such materials as light 
fabrics are very combustible, but books in which the 
paper leaves are pressed closely together, and bales of 
fabrics, are very difficult to burn ; and when a warehouse 
has been burned, whilst all the loose goods are destroyed, 
it is quite common to find bales of the same materials only 
singed on the outside. Heavy beams of wood make fireproof 
floors, and saw-dust or coal-dust thrown on a fire will often 
extinguish it. 

Proportion of Combustible. — In order that combustion 
may take place, the combustible and air must be present in — 
within certain limits — definite proportions. This is not so 
noticeable in the case of solid or liquid fuels, or of gas burned 
in a flame, because, owing to the circulation set up in the air, 
the proportions to some extent adjust themselves. It is, 
however, well seen in the case of mixtures of gases. If coal- 
gas and air be mixed in certain proportions a violently ex- 
plosive mixture results ; but there may be a large quantity of 
gas in the air, enough to be detected by the smell and to pro- 
duce chemical and physiological effects, and yet the mixture 
will not explode on applying a light. The presence of a large 
quantity of inert matter in a fuel may much hinder or even 
prevent combustion, whilst the presence of a comparatively 
small quantity of carbon dioxide in the air will prevent it 
supporting combustion. Professor Clowes has recently shown 
that air which contains about 4 per cent of carbon dioxide, 
the oxygen being reduced by a like amount, will extinguish 
ordinary combustibles, such as candles or oil flames. 1 Marsh- 

1 J.S.C.I. vol. xiv. p. 346. 



4 FUEL 

gas must be mixed with at least 17 times its own volume of 
air to form an explosive mixture. 

Temperature of Combustion. — For combustion to take 
place a certain temperature, varying with the nature of the 
combustible, is necessary. A mixture of hydrogen and oxygen 
in explosive proportions will remain inert for any length of 
time until a portion of the mixture is raised to about 1100° F. 
(590° C), when ignition will at once take place. Coal-gas 
ignites in air at a red heat. Many of the metals are not 
acted on by dry oxygen at ordinary temperatures, but if they 
be heated to redness some of them burn, as in the case of 
magnesium, with great brilliance. On the other hand, phos- 
phorus ignites at such a low temperature that for safety it is 
always kept under water or otherwise protected from contact 
with the air, and some substances have such affinity for 
oxygen that they take fire on coming in contact with it. 

The temperature at which combustion can take place 
varies also with the condition of the combustible. Lead and 
iron can be obtained in such a fine state of division that they 
take fire spontaneously in air at ordinary temperatures. 1 

Continuous Combustion. — In some cases when a sub- 
stance has been ignited it will continue to burn, in others it 
will go out as soon as the external source of heat is removed. 
This depends on the relationship which exists between the 
heat evolved by combustion and the temperature of ignition. 
If the heat evolved be sufficient to maintain the temperature 
above the ignition point the combustion will continue, if not 
it will cease. 

Combustibles and Supporters of Combustion. — The 
fuel or substance which burns is usually called a combus- 
tible, and the oxygen of the air is called a supporter of 
combustion. These terms, though convenient, are not 
strictly correct, except in so far as they indicate an accident 
of position. Combustion is a mutual action in which both 
substances play an equal part, which being combustible and 
which supporter of combustion depending on circumstances. 

I These fine powders may be allotropic modifications of the metals. 



COMBUSTION 5 

When a solid combines with a gas, the gas surrounds it, and 
is therefore regarded as a supporter of combustion. When a 
mixture of a combustible gas, such as hydrogen, and air is 
exploded it is impossible to say that either is the combustible « 
rather than the other ; but when gas is burnt at a jet the 
flame is surrounded by the excess of air, which is therefore 
called a supporter of combustion. It is quite simple to 
arrange experiments so as to burn air in coal-gas or oxygen 
in hydrogen, and thus reverse their usual positions. 

Complete and Incomplete Combustion. — All combus- 
tibles in common use are composed chiefly of carbon (C), 
usually combined with hydrogen (H), oxygen (0), and some- 
times small quantities of other elements, but the carbon and 
hydrogen are always the valuable constituents. 

When a combustible burns, the combustion may be either 
complete or incomplete. It is complete when all the com- 
bustible constituents are oxidized to their highest state of 
oxidation, and it is incomplete when any fuel is either left 
unconsumed, or passes away combined with less oxygen than 
the maximum with which it is capable of combining. 

In the case of hydrogen, there is only one compound that 
can be formed — water, H 2 ; and therefore, if the com- 
bustion be incomplete, some of the hydrogen must remain 
unconsumed. 

In the case of carbon, the highest state of oxidation is 
carbon dioxide, C0 2 ; but there is also another oxide, carbon 
monoxide, CO, which contains, for the same amount of carbon, 
only one-half as much oxygen. When carbon is incompletely 
burned, therefore, either carbon may be left unconsumed, or 
carbon monoxide may be formed and pass away with the 
products of combustion. Both carbon dioxide and carbon 
monoxide are colourless gases, so that it is often not easy to 
decide whether combustion is complete or not. 

The combustion of carbon commences at a comparatively 
low temperature ; at about 750° F. (400° C.) the product is 
almost entirely carbon dioxide ; as the temperature rises the 
rate of combustion increases, and the proportion of carbon 



6 FUEL 

monoxide formed increases till, at 1830° F. (1000° C), the 
product is almost entirely this gas, which, if the air supply be 
sufficient, is rapidly burned to carbon dioxide. It is for this 
reason that carbon at low temperatures simply smoulders, 
whilst at very high temperatures it burns with a flame. 

The combustion of hydrocarbons is much more complex. 
If the- combustion be quite complete, the products are water 
and carbon dioxide ; but if it be incomplete, what products 
will be formed depends on circumstances. Many hydro- 
carbons dissociate or split up into simpler hydrocarbons with 
separation of hydrogen, as, for instance, ethylene, C 2 H 4 , 
which goes partly to hydrogen and acetylene, C 2 H 2 . The 
hydrogen burns to water, and the acetylene, partially escap- 
ing as such, imparts a most unpleasant odour to the products 
of combustion of incompletely-burnt hydrocarbon gases. 
The carbon will be burned to carbon dioxide, or a mixture 
of this and carbon monoxide. Under some conditions carbon 
may also be separated by dissociation in the solid form as 
soot. 

Incomplete combustion of any kind always means con- 
siderable loss of heat. 

Conditions of Complete Combustion. — In order to 
ensure complete combustion, three things are essential : the 
air supply must be sufficient, the air must be brought into 
intimate contact with the fuel, and the temperature must be 
kept up to ignition point until combustion is quite complete. 
Either insufficient air supply or too rapid cooling is the usual 
cause of incomplete combustion. 

Flame. — Fuels burn in very different ways. Some, as 
for instance charcoal at low temperatures, burn with a glow, 
evolving but little light ; others, such as the metal magnesium, 
burn with a very brilliant light, but with no flame ; others, 
like hydrogen, burn with a non-luminous flame ; and lastly, 
some, like coal-gas, burn with a bright luminous flame. All 
combustible gases — and gases only — burn with a flame. 
There are some apparent exceptions to this, but they are only 
apparent ; and whenever a solid or liquid seems to burn with 



COMBUSTION 



a flame, it is because it is converted into gas either before or 
during combustion. " Flame is gas or vapour, the surface 
of contact of which with the atmospheric air is burning with 
the emission of light " (Percy). As combustion only takes 
place at the surface of contact, the flame must be hollow. 

A simple flame is one in which there is only one product 
of combustion, and a compound flame is one in which there 
are two or more. Almost all flames used in the arts are 
compound, the only 
examples of simple 
flames being those of 
hydrogen and carbon 
monoxide. 

Simple Flame. — 
As an example of a 
simple flame a jet of 
hydrogen burning in 
air may be taken. 
As the hydrogen 
escapes from the jet 
it displaces the air 
and then diffuses into 
or mixes with it, and 
in the space where 

the gases mix combustion takes place. In the centre of the 
flame, therefore, will be a core of unburnt gas, outside will 
be the air, and between is the zone of combustion, or the 
flame. 

Compound Flames. — With compound flames the re- 
actions are much more complex, and it is often difficult to 
determine the exact changes which take place. The com- 
pound flames of most practical importance are those obtained 
by the combustion of various hydrocarbon gases. The fuel 
may be used in the form of gas from a burner, in the solid 
form as a candle, or in the liquid form as in the case of the 
burning oils. In the last two cases the combustible is drawn 
up by the wick by capillary attraction, gasified by the heat 




Fig. 1.— Gas Flame. 



8 FUEL 

evolved during combustion, and the gas is burned ; indeed, 
candles and lamps may be regarded as combined gas producers 
and burners. 

The structure of a compound flame is much the same as 
that of a simple one. In the centre is a core of unburnt gas, 
outside is the air, and between the two is the zone of com- 
bustion or the flame ; but this zone is much more complex 
than in a simple flame, the combustion in the inner portions 
being usually incomplete. 

Luminosity of Flame. — Most of the flames produced by 
hydrocarbons are more or less luminous, and the cause of this 
luminosity has given rise to a vast amount of discussion. 
Clearly the luminosity is not due to temperature alone, for 
a hydrogen flame, especially when formed by a mixture of 
hydrogen and oxygen, is intensely hot, but almost non- 
luminous ; and it is quite possible to burn coal-gas, e.g. in 
the Bunsen burner, in such a way as to give a very hot, 
but non-luminous flame. 

Davy suggested that the luminosity of flame was due to 
the separation of particles of solid carbon by incomplete 
combustion within the flame, which, being heated to intense 
whiteness, evolve light. This theory has been generally 
accepted, and in its favour many facts may be quoted : 

1. If solid matter be introduced into a hot, non -luminous 
flame, light is evolved. A cylinder of lime, for instance, 
placed in an oxy-hydrogen flame gives the brilliant lime-light; 
a mantle of thoria and ceria suspended in a non-luminous 
Bunsen flame is the Welsbach incandescent burner now so 
largely used for illumination purposes. 

2. If a cold surface be held in an ordinary luminous flame 
it becomes covered with a black deposit of solid carbon or 
soot. 

3. Many substances which burn with the formation of 
solid products of combustion, e.g. magnesium or zinc, give 
an intense white light. 

4. Luminous flames when examined with a spectroscope 
give a continuous spectrum. 



COMBUSTION 9 

5. , When sunlight is reflected from hydrocarbon flames, 
it is polarized exactly in the same way as light reflected from 
solid carbon particles suspended in air. 

On the other hand, Frankland contended that — at least 
in many cases — luminosity was due to the presence not of 
solid particles but of very dense gases or vapours. In 
support of this view it may be urged : 

(1) That the luminosity of many flames is much increased 
under pressure, even a flame of hydrogen becoming luminous 
at high pressures, and that under reduced pressures the 
luminosity of ordinary luminous flames is much reduced. 

(2) That many substances, e.g. phosphorus and arsenic, 
burn with a very luminous flame, though at the temperature 
of combustion the products are gaseous. Hydrogen pro- 
duces water having a vapour density of 9 (H =1), and the 
flame is non-luminous. Phosphorus produces phosphoric 
anhydride, P 2 5 , having a density of 71, and the flame is 
luminous ; and arsenic, which produces arsenious oxide, 
As 4 6 — vapour density 198 — also burns with a luminous 
flame. Therefore whether the flame will be luminous or not 
seems to depend on the density of the products of combustion. 

(3) Soot is not pure carbon, but always contains hydro- 
gen ; and further, the fact that soot is deposited does not 
prove that it existed as such in the flame, as it may have 
been produced by the decomposition of dense hydrocarbons 
present. 

(4) Gases under great pressure give much more complex 
spectra than under ordinary conditions, becoming banded, 
and ultimately tending to become continuous. 

For these reasons it has been urged that luminosity of 
ordinary hydrocarbon flames may be due to the presence of 
very dense hydrocarbons, which under suitable conditions 
split up into carbon and hydrogen or light hydrocarbons, 
which are then burned. 

Profs. Lewes' and Smithells' Researches. — Professors 
V. B. Lewes and A. Smithells investigated the question 
of the luminosity of coal-gas and similar flames, and 



10 



FUEL 



whilst their work confirms the view that the luminosity 
is due to separated carbon particles, it has thrown fresh 
light on the reactions within the flame by which these are 
separated and the conditions under which luminosity can 
be produced. 

Prof. Smithells describes x the structure of an ordinary 
luminous gas flame as consisting of four parts, which, for 
convenience, may be taken in the inverse 
order to that in which they are given by 
him : 

(4) A dark inner core or region, 
consisting principally of unburned gas, 
mingled with some products of com- 
bustion which have diffused in from the 
surrounding parts (c in Fig. 2). 

(3) A yellow luminous portion, mark- 
ing the region in which hydrocarbons 
are undergoing decomposition, the heat 
producing the dissociation being largely 
derived from the outer zones (a). 

(2) An inner light-blue portion, visible 
at the base of the flame (d) ; and 

(1) An outer sheath or mantle (b) ; 
these parts (1 and 2) corresponding to 
the outer and inner flame-cones of the 
Bunsen burner, and marking the region 
where the gas is undergoing combustion 
in presence of excess of air. 

The explanation which has usually been given of the 
phenomena of luminosity is something like this : The gas 
coming into the air is at first mixed with only a very limited 
supply of air ; the hydrocarbons cannot be completely 
burned, therefore the hydrogen burns, forming water, and 
the carbon is liberated and heated to incandescence by the 
heat evolved by the combustion of the hydrogen. 

This description has been shown to be incorrect in at least 

1 J. S.C.I, vol. x. p. 994. 




Fig. 2.— Candle Flame. 



COMBUSTION 11 

two points : (1) the order of combustion, and (2) the source 
of the heat. 

1. The hydrogen does not burn first, in the case of 
methane at any rate ; the reaction being, as pointed out by 
Dalton, CH 4 + 20 = CO + H 2 + 2H — water, carbon monoxide, 
and hydrogen being thus formed. But as carbon monoxide 
and water can mutually decompose each other, CO + H 2 = 
C0 2 + 2H, a further reaction may take place till the system 
attains equilibrium, the conditions of which, " according to 

Dixon, are expressed by the coefficient -^ ^ = 4. This 

v>U 2 x -H-2 

is subject to certain conditions of temperature and dilution." 1 
These reactions, however, probably take place only to a 
small extent in the inner luminous part of the flame. 

The source of the heat, therefore, is to be looked for, not 
altogether in this partial combustion, but in transmission 
from the outer zone, where the temperature is very high. 

2. The constituent of coal-gas to which the luminosity is 
mainly due is ethylene, C 2 H 4 , and perhaps some of its higher 
homologues. This at high temperatures (1500 - 1800° F.) 
splits up, yielding acetylene and methane, 3C 2 H 4 =C 2 H 2 + 
CH 4 , the acetylene then polymerizing into more complex 
hydrocarbons. At higher temperatures (above 2130° F.) 
no polymers are formed, but only acetylene, and at that 
temperature methane also dissociates, yielding acetylene and 
hydrogen, 2CH 4 = C 2 H 2 + 2H, so that all the hydrocarbons 
present will have split up into acetylene and hydrogen. At 
still higher temperatures acetylene itself splits up into carbon 
and hydrogen, this change taking place at about 2430° F. 

The various hydrocarbons, as is well known, burn with 
very different degrees of luminosity. The flame of methane, 
CH 4 , is very slightly luminous, that of ethylene, C 2 H 4 , is 
more luminous, whilst that of acetylene is intensely brilliant. 
That the luminosity is not due merely to the amount of 
carbon which the combustible contains is shown by the fact 
that in equal volumes of gas ethylene and acetylene contain 

1 J.S.C.I. vol. x. p. 994. 



12 FUEL 

the same weight of carbon, whilst benzene, C 6 H 6 , which burns 
with a luminosity much inferior to that of acetylene, contains, 
in the gaseous condition, three times as much carbon. 

Neither is the luminosity due to temperature alone, as 
has been already shown. 

It is now possible to form some idea of what actually 
takes place in a luminous gas flame. The inner blue core 
must be regarded as altogether unburned gas, for in it no 
combustion is taking place, but the temperature is rising, 
much heat being received by radiation from the outer zones 
of the flame, and the hydrocarbons being to some extent 
dissociated. As the temperature rises, dissociation takes 
place to a greater extent, till all the hydrocarbons, or nearly 
so, are converted into acetylene, and then the acetylene 
itself undergoes dissociation. This dissociation evolves 
heat, and at once brings the separated carbon up to vivid 
incandescence. As the products of these reactions pass 
outwards they are burned, the temperature therefore rising 
to the edge of the flame, and the combustion is completed 
in the very hot but feebly luminous mantle. 

The luminosity, therefore, seems to depend not so much 
on the actual amount of carbon contained in the gas, or on 
the temperature, as on the readiness with which the gases 
present form acetylene or some other hydrocarbon which 
will similarly dissociate. 

The luminosity of an acetylene flame is much reduced by 
the admixture of other gases, even though they themselves 
are combustible and evolve a large quantity of heat ; as, 
for instance, hydrogen and carbon monoxide. The presence 
of such gases not only reduces the luminosity of the flame, 
but enormously raises its dissociation temperature, which is 
the point at which luminosity begins ; thus — 

Percentage of 
Acetylene. Hydrogen. Temperature of Luminosity. 

100 1440° F. 

90 10 1650 

80 20 1830 

10 90 3090 

The above " acetylene theory " of the chemical reactions 



COMBUSTION 13 

on which luminosity of flame depends is not now generally 
accepted. 1 In any case the reactions are complex. 

Non-luminous Combustion. — If coal-gas, or any other 
gas which usually gives a luminous flame, be burnt in such a 
way that excess of oxygen penetrates into every part of the 
flame, and the acetylene burns before it can undergo dis- 
sociation, the flame will be non-luminous. Thus, if a gas 
flame be turned very low it is non-luminous, so also is candle 
flame when the wick is very short. The best means of 
obtaining a non-luminous flame is the Bunsen burner. 

The Bunsen Burner. — This burner consists of a tube, 
usually about f " in diameter and 3J" long, though the size 
may be varied within wide limits. Gas is admitted to the 
bottom of the tube, and just above the jet by which the gas 
enters are holes for the admission of air. The air (usually 
2J volumes) mixes with the gas, and the mixture burns with 
a hot non-luminous flame. 

" When a Bunsen burns under normal conditions it has a 
bluish central zone, but if the air supply be largely in excess 
of that required for non-luminous combustion, the flame 
becomes smaller and fiercer with the formation of a green 
central zone." 2 

The cause of the non-luminosity of the flame has usually 
been attributed to the more perfect combustion of the hydro- 
carbons due to the excess of oxygen in the interior of the 
flame. Professor Lewes has shown that this is not by any 
means necessarily the case, as nitrogen, carbon dioxide, and 
other inert gases also prevent luminosity, dilution, as already 
remarked, very much retarding the dissociation of acetylene, 
and therefore the production of luminosity. It is this 
dilution which is generally efficient in preventing luminosity 
in the " Bunsen " ; but if the air supply be too large then 
oxidation takes place rapidly, and the inner cone changes in 
appearance. The temperature of the flame is a little higher 
when the diluent is air than when it is nitrogen. 

1 W ? A. Bone and H. F. Coward, J. Chem. Soc. 1908, p. 1197. 
5 V. B. Lewes, J.S.C.I., 1892, p. 231, 



14 FUEL 









Air. 




Nitrogen. 


\ inch above burner 




54° 


C. 129° F. 


30° 


C. 


86 


*-~2 j> >» »» 


. 


175 


347 


111 




231 


Tip of inner cone . 




1090 


1990 


444 




831 


Centre of outer cone 




1535 


2795 


999 




1830 


Tip of outer cone 




1175 


2150 


1150 




2100 


Side of outer cone 


level with 












tip of inner cone 


. 


1335 


2435 


1235 




2255 



If the supply of air be too small then a luminous point 
appears at the tip of the inner cone. 

It does not follow because the flame is non-luminous 
that combustion is complete ; it frequently happens that the 
ingress of air has cooled the gases below ignition point, and 
not " inconsiderable portions of methane, carbon monoxide, 
acetylene, and even hydrogen escape unburnt," both from 
non-luminous and luminous flames. 

Professor Lewes thus describes the structure of an 
ordinary luminous flame, and the actions which render it 
non-luminous in the Bunsen : 

" 1. The inner zone, in which the temperature rises from 
a comparatively low point at the mouth of the burner to 
about 1000° C. (1830° F.) at the apex of the zone. In this 
portion of the flame various decompositions and interactions 
occur, which culminate in the conversion of the heavier 
hydrocarbons into acetylene, carbon monoxide being also 
produced. 

"2. The luminous zone, in which the temperature ranges 
from 1000° C. (1830° F.) to 1300° C. (2370° F.). Here the 
acetylene formed in the inner zone becomes decomposed by 
heat with liberation of carbon, which at the moment of 
separation is heated to incandescence by the combustion of 
the carbon monoxide and hydrogen, thus giving luminosity 
to the flame. 

"3. The extreme outer zone. In this part of the flame, 
the combustible gases meeting air, combustion takes place, 
making this the hottest part of the flame ; but towards the 
outer part of this zone, combustion being practically com- 
pleted, the cooling and diluting influence of the entering air 



COMBUSTION 15 

renders a thin layer of the flame non-luminous, finally 
extinguishing it. This description of a luminous flame is of 
necessity far from complete." 

" The various actions which tend to cause the loss of 
luminosity in a Bunsen burner may be summarized as 
follows : 

"1. The chemical activity of the atmospheric oxygen 
which causes loss of luminosity by burning up the hydro- 
carbons before they, in their diluted condition, can afford 
acetylene. 

" 2. The diluting action of the atmospheric nitrogen, 
which, by increasing the temperature necessary to bring 
about the partial decomposition of the hydrocarbons, pre- 
vents formation of acetylene, and in this way will by itself 
cause non-luminosity. In the normal Bunsen flame it acts 
by doing this until destruction of the hydrocarbons by 
oxidation has taken place. 

"3. The cooling influence of the air introduced, which is 
able to add to the general result, although the cooling is less 
than the increase in temperature brought about by the 
oxidation due to the oxygen of the air. 

"4. In a normal Bunsen flame the nitrogen and the 
oxygen are of about equal importance in bringing about non- 
luminosity ; but if the quantity of air be increased oxidation 
becomes the principal factor, and the nitrogen practically 
ceases to exert any influence." 

The amount of air supplied to the ordinary Bunsen is 
quite insufficient to support combustion without the air 
outside. 

Propagation of Flame. — If a long glass tube, closed at 
one end, be taken and filled with an explosive mixture, say of 
coal-gas and air, and a light be applied at the open end, the 
flame will run down the tube with a definite and usually 
measurable speed, combustion not taking place instantane- 
ously, but the ignition being transmitted from molecule to 
molecule at a comparatively slow rate. The speed at which 
the flame travels is called " the speed of propagation of the 



16 FUEL 

flame," and combustion thus taking place has been called an 
" explosion of the first order." 

If, instead of a closed tube filled with gas, a tube open at 
both ends be used, and the mixture be made to flow through 
it — if the gas be lighted so that the ignition has to travel in 
the opposite direction to that in which the gas is flowing, its 
speed of transmission will be reduced, and will be the differ- 
ence between the speed of propagation and the rate at which 
the gas is flowing, if the former be greater than the latter. 
If the rate of flow of the gas be very slightly in excess of the 
speed of propagation of the explosion, the flame will remain 
just at the mouth of the tube, and if it be much greater there 
will be a more or less long flame. Deville made a series of 
most interesting experiments on the rate of propagation of 
flames, and it is to his work, and that of Bunsen, that we 
owe most of our knowledge of the subject. He burnt a 
mixture of two volumes of carbon monoxide and one volume 
of oxygen — the gases therefore being almost exactly in the 
proportions required for complete combustion — at a jet 
having an area of 5 square millimetres. A flame 70 to 
100 mm. high was formed, which consisted of two portions, 
an inner cold core, 10 mm. high, and an outer flame zone. 
It is obvious that in this case the inner core was not due to 
the absence of oxygen for combustion, but to the fact that 
the gases were travelling forward at such a speed that the 
ignition could not travel backwards, and ignite the mixture 
in the tube ; and no doubt had the rate of flow been 
diminished the flame would have grown smaller and ulti- 
mately lighted back. 

When a light is applied to an explosive mixture, an 
explosion usually takes place, the violence of which depends 
very largely on the speed at which the ignition is propagated. 
Bunsen found that in the case of a mixture of two volumes 
of hydrogen to one of oxygen the flame was propagated at 
the rate of 34 metres (37 yards) per second, the velocity being 
much reduced by the presence of inert gases. With marsh - 
gas (CH 4 ) and air the greatest velocity was -56 metre (22 



COMBUSTION 17 

inches) per second, and this was attained with a mixture of 
one volume of marsh-gas to eight and a half volumes of air, 
a mixture which contains less oxygen than is required for 
complete combustion. A flame with a velocity of about 
four and a half metres (4-9 yards) per second will pass 
through the wire-gauze ordinarily used for safety-lamps. 

Explosion. — If an explosion takes place, its violence, as 
remarked above, depends on the rate at which the ignition is 
propagated. If it is in a closed vessel, vibrations may be 
set up which will enormously increase the speed of propaga- 
tion of the ignition, sometimes bringing it up to many 
hundred feet per second. Explosions of this kind are called 
by Wright " explosions of the second order," and it is to 
them that most of the damage done by explosions is due. 

The velocities of explosion found by Dixon for mixtures 
with oxygen in the exact proportions for complete combus- 
tion were : 

Hydrogen. Acetylene. Ethylene. Methane. 

2821 2391 2364 2322 

metres per second. 

Dissociation. — Referring back to Deville's flame with a 
mixture of carbon monoxide and oxygen, the fact that the 
ignition takes time to travel explains why the flame does not 
run back down the tube, but it does not explain why it 
spreads itself out into a flame of the ordinary form instead 
of at once igniting when it is released from the tube. This 
is due to dissociation. 

The products in all ordinary cases of complete combus- 
tion are carbon dioxide and water, these being formed by 
the combustion of carbon, carbon monoxide, and hydrogen. 
If carbon dioxide and water be heated sufficiently strongly 
they are split up or dissociated into their constituents, water 
being broken up into hydrogen and oxygen, and carbon 
dioxide into carbon monoxide and oxygen. It is quite 
evident that if hydrogen and oxygen, or carbon monoxide 
and oxygen, be brought together at a temperature higher 
than that at which this dissociation takes place, combina- 

(D107) £ 



18 



FUEL 



tion will be impossible, and therefore there can be no com- 
bustion. 

If a mixture of hydrogen and oxygen be inclosed in a 
strong vessel and exploded, it is possible from a knowledge 
of the heat which will be evolved on combustion to calculate 
the pressure which the steam formed should exert. When 
the experiment is made it is always found that the pressure 
produced is less than the theoretical amount. The main 
reason for this is : that combination is not instantaneous. 
As it progresses the temperature rises till the dissociation 
point is reached, when it can go no further, for this is the 
maximum temperature at which combustion is possible. 
As heat is lost by radiation, the gases cool and further 
combination takes place, and so on till combustion is com- 
plete. Another reason is the high and rather uncertain 
specific heat of steam at high temperatures. 

Deville's experiment with the carbon monoxide and 
oxygen flame illustrates this very well. He carefully took 
the temperatures of all parts of the flame, and the results 
are recorded in the table. 



Height above 
Burner. 


Temperature. 


Percentage 
of Gases. 


mm. 
67 
54 
44 
35 
28 
18 
15 
12 
10 



inches. 

2-64 

213 

1-73 

1-38 

110 

•71 

•59 

•47 

•39 


Above melting point of silver 
Melting point of gold 
Commencing white-heat of platinum 
White -heat of platinum . 
Strong white-heat of platinum 
Intense white -heat of platinum 
Incipient fusion of platinum . 
Melting point of platinum 
Sparkling of melted platinum 




CO. 
•2 
6-2 
10 
173 
19-4 
29 
40 
47 
553 
64-4 


0. 
21 3 
28- 1 
20 
24-8 
26-5 
25-1 
32-9 
36 
353 
333 


CO,.' 
78-5 
65-7 
70 
579 
541 
45-9 
27- 1 
17 
94 
23 









These figures at once explain the whole phenomena. As 
soon as combustion begins the temperature rises, and at the 
apex of the inner cone 10 mm. (-39") above the burner it 
has reached the melting point of platinum, which is above 
the dissociation point of carbon dioxide ; so that no further 
combination is possible till the gases cool. This they do as 



COMBUSTION 19 

they rise, and combustion again can take place, and this 
goes on till at the top of the flame all the carbon monoxide 
has disappeared and combustion is complete. From the 
very first the flame contains excess of oxygen, as some of the 
carbon monoxide is burned by the oxygen of the air. The 
length of the flame, therefore, is due to dissociation. 

The dissociation temperature does not seem to be an 
absolutely fixed point, but varies with circumstances, it 
being in general raised by the presence of inert gases, and 
considerably lowered by contact with hot solids. 

Dissociation plays a very important part in the practical 
applications of combustion. 

Smoke. — Many hydrocarbon flames under certain con- 
ditions become smoky, the smoke being due to the separation 
of carbon under conditions which do not allow of its com- 
bustion. The cause of smoke is always imperfect combus- 
tion, due either to a deficient supply of air or to reduction of 
temperature. It is easy to see how the latter can be brought 
about. Air diffusing into a flame soon cools it ; and if there 
be solid carbon in it this is likely to escape combustion. 
Smoke is always accompanied by other products of incom- 
plete combustion. 

Domestic Fire. — As an example of some of the causes 
which lead to smoke, an ordinary domestic fire may be con- 
sidered. The whole question of the production and preven- 
tion of smoke will be discussed later. 

Suppose, in the first instance, the fireplace to be full of 
glowing coke. As the air enters, combustion takes place and 
carbon dioxide is formed, C + 20 = C0 2 , together with some 
carbon monoxide either formed directly, C + = CO, or by 
the reduction of carbon dioxide, C0 2 + C = 2C0. This 
coming into the air at the top of the fire burns with its 
characteristic blue flame, carbon dioxide being produced, 
CO + = C0 2 , and the combustion is complete. If now the 
fire be made up in the usual way, by throwing cold coal on 
the surface, all is changed. The reactions at the lower part 
of the fire go on as before, but the carbon monoxide in passing 



20 FUEL 

through the coal is cooled below the point at which ignition 
can take place. At the same time the heat below begins to 
act on the coal, and destructive distillation commences, 
gases, and tarry matter which forms a dense yellow smoke, 
being given off ; being cool, these do not ignite, but pass 
unburned to the chimney. After a time, as the heat pene- 
trates, or perhaps when the fire is stirred, these gases ignite 
and burn with the bright flame characteristic of coal-gas. 
Smoke always indicates loss of fuel, not only because of the 
actual carbon which it contains, but also because the con- 
ditions which favour the production of smoke always favour 
the escape of combustible gases. 

Heating by Contact or Radiation. — All fuels are burnt 
for heating purposes, and the methods of transferring the 
heat from the incandescent fuel to the object to be heated are 
of importance. Heat may be transferred in two ways — (1) 
by contact, as when a bar of iron is placed in a hot coke fire 
surrounded by the burning coke ; (2) by radiation, as when 
an article is heated by being held in front of a fire. In many 
cases heating is necessarily by contact, as, for instance, in 
the blast-furnace, where the charge is heated by contact with 
the hot ascending gases, or with the hot fuel ; and in others 
it is very largely by radiation, as when a room is heated 
by an ordinary house fire ; and there are others in which 
both methods come into play. 

Heating by contact of flame is not possible, except when 
the substance being heated is at a moderately high tempera- 
ture. When flame is playing under a boiler it seems as if 
the heating were due to the actual contact of the flame. 
This is not the case, as the flame cannot touch the com- 
paratively cold surface — kept cold by the contact of the 
water — but is separated from it by a thin cold layer, across 
which heat can only travel by radiation. Gases are, as a 
rule, very bad radiators ; hence the Bunsen burner, though 
very satisfactory for heating small articles with which the 
flame can come into contact, is a very poor source of heat 
for heating by radiation, and when it is so used, as in many 



COMBUSTION 21 

gas fires, iron, asbestos, or other material is fixed so as to be 
heated by the flame and made to radiate, sometimes at the 
cost of hindering complete combustion. Water vapour is a 
very good radiator, and its presence no doubt materially 
increases the radiating power of many non-luminous flames. 
Carbon is one of the best radiators, and therefore the luminous 
flame with its separated incandescent carbon is much more 
efficient for heating by radiation than the non-luminous 
Bunsen flame which has been shown to have a radiation 
efficiency of about 10 to 15 per cent. 

Amount of Air required for Combustion. — If we know 
the composition of a fuel it is an easy matter to calculate 
the amount of air which it requires for its complete com- 
bustion. 

The air for all practical purposes may be taken as con- 
taining 21 per cent by volume and 23 per cent by weight of 
oxygen. When carbon burns to form carbon dioxide, 12 
parts of carbon combine with 32 parts of oxygen to form 
44 parts of carbon dioxide ; so that 1 part of carbon will 
combine with 2-67 parts of oxygen to form 3-67 parts of 
carbon dioxide. If c be the percentage of carbon contained 
in a fuel which contains no other combustible material, 
then W, the weight of oxygen required for the combustion 
of 1 lb., will be 

(1) W= C -^- 7 =cx.0267. 

The weight of air A will be 

/ftX A ex 2-67 100 ex 2-67 

W ^=l00^ x 23 = -23- =CX - 116 - 

One part of hydrogen when it burns combines with 8 
parts of oxygen to form 9 parts of water, so that the weight 
W of oxygen required for the combustion of 1 lb. of a fuel 
containing h per cent of hydrogen and no other combustible 
would be 

(3) W-^i 



22 FUEL 

and A, the weight of air, 

< 4 > A= ioo x T3 = ^ =Ax - 348 - 

If the fuel contains c per cent of carbon and h per cent 
of hydrogen, then W, the weight of oxygen required for the 
combustion of 1 lb. of the fuel, would be 

/e , TT7 ex 2-67+^x8 

(5) w = loo • 

and the weight of air 

(6) A=cx-116+fcx-348. 

If the fuel contains o per cent of oxygen, then h must 
be taken to stand not for the total but for the available 
hydrogen (h -\o). 

As one cubic foot of air under the normal conditions of 

temperature and pressure may be taken to weigh -0809 lb. 

(566-3 grains), the volume of air required for combustion 

would be 

c x-116+/&x-348 

* ' " -0809 

If the air be at any other temperature and pressure, this 
must be taken into account. 

The volume of a gas varies inversely as the pressure, so 
that if the normal pressure be taken as 29-92 x inches of 
mercury (14-7 lbs. per square inch), the volume v under the 
normal pressure will become v' at the pressure p, and 

(8) ^ - «***** . 

P 

If 760 mm. be taken as the standard, and the pressure p 
be measured in millimetres of mercury, the formula becomes 

(8') *-**™ m 

p 

The law according to which gases expand by heat may be 
expressed in various ways ; probably the simplest is to say 

1 For ordinary purposes 30 inches may be taken and 30 substituted 
for 29-92 in the equations. 



COMBUSTION 23 

that the volume is proportional to the absolute temperature. 
The absolute zero is for the Fahrenheit scale - 459, and for 
the Centigrade scale - 273, so that any temperature * on the 
Fahrenheit scale will be 459 +t on the absolute scale in F. 
degrees, and *' on the Centigrade scale will be 273 + *' on the 
absolute scale in C. degrees. 1 

A volume of gas v at 32° F. would therefore become at 
t° F. 

4.KQ i / 

(9) t>-Vx ^ 2 , or v=V(l +0-002037). 

On the Centigrade scale the volumes would be 

(9') v =Vx 2 ^^=Vx(l + -003665*). 

Combining the two equations, the volume of air v at 32° F., 
and 29-92 inches barometer, would become at *° F. and a 
pressure of p inches of mercury v' t and 

, 1A v , Tr 29-92 459+* 
(10) ,-Vx— x-gj- 

= v 29-92 x(459+*) 
px491 

OQ.QO 

orv'=Vx — x (1 + -002037* - 32) ; 

and for Centigrade degrees and millimetres 

/1A>N / XT 76 ° 273+ ^ 
(10) ^'=Vx— x— 3 , 

or =Vx-°x(l+ -003665*). 

The following formulae are very similar to those given 
above, and are quite near enough for practical purposes. 
They are calculated for air containing an average amount of 
moisture. 

c is the percentage of carbon in the fuel, and h the per- 

1 The absolute temperature may also be determined from thermo- 
dynamic principles, almost identically the same zero being obtained. 



24 FUEL 

centage of available hydrogen ; A and V the weight and 
volume of air required as before ; then 

(11) A = -12c + -36ft; 

taking one cubic foot of such air as weighing -07639 lb. the 
volume v would be 

(12) V = l-57c+4-7lA. 

In practice excess of air must be used, so that the figures 
found as above must be multiplied by a factor. This will be, 
for gas furnaces about 1-5, for good grates about 2, and for 
defective grates 3 or more. 

Products of Combustion. — The weight of the products 
of combustion will of course be the weight of the fuel con- 
sumed together with the weight of the air supplied ; so that 
if W" is the weight of the products of combustion, A =the 
weight of air, F the weight of fuel, and a the weight of the 
non-combustible portion or ash, then 

(13) W" =A+F-a. 

The products of combustion will be carbon dioxide from 
the fuel, water partly formed by combustion of the hydrogen 
and partly moisture contained in the fuel, the nitrogen from 
the air and the excess of air ; so that if c, h, o, and w be the 
percentages of carbon, hydrogen, oxygen, and water con- 
tained in the fuel, and E the excess of air, the weight of the 
products of combustion will be 

n > w ,„ c x 3-67 + h x 9 + {c x 2-67 +(h- |o)8}f| +w + E 
{ ' ~ 100 

Heat carried away by Gases. — If it be required to 
know the heat carried away by the gases, this can be obtained 
by multiplying the products of combustion by their specific 
heats and the temperature at which they escape. All that is 
required in practice is to know the amount of heat lost which 
could be usefully employed, and as heat below 100° would be 
of little value no note need be taken of the latent heat of 
steam. 



COMBUSTION 25 

The heat carried away will be 

tin\ K ^ {3-67c x -2387 +(97? +w)x -4805 + (267 +8^-^o)xT,|x -2485 + Ex -2375 } t . 
V 10 ^ 100 

and if it be required to take into account the latent heat of 

,, (9h+w) x966 , , , , , 

steam, then * — '- must be added. 

A simpler and sufficiently accurate method is to take the 
weight of the products of combustion by (13) and multiply 
this by -25, which is approximately the average specific heat 
of the gases, and by the temperature, so that 

(16) H=(A+F-a)-25x«. 

Volume of Products of Combustion. — When carbon 
burns to carbon dioxide the carbon dioxide formed occupies 

the same bulk as the oxygen consumed (C +20 = CQ 2 ). 

i i i i i i 

When carbon monoxide is formed the volume is twice that of 

the oxygen (C + = CO). When hydrogen burns, the volume 

D DD 
of the gas is two-thirds of that of the component gases or 

twice that of the oxygen (2H+0=H 2 0). With gaseous 

i i i □ m 
fuels the reactions are more complex. Marsh-gas yields pro- 
ducts which occupy the same volume as the gas burned and 

the oxygen used (CH 4 +40 = C0 2 +2H 2 0). With ethylene, 

j i i I i l i i i I i I 
I i 1 1 i 1 

C 2 H 4 , the products also occupy the same volume as the gas 
and oxygen, and with acetylene three-quarters of the volume. 
In general, therefore, for solid fuels the volume of the 
products of combustion may be taken as being equal to that 
of the air supplied, and with gaseous fuels as being equal to 
the sum of the volumes of the gas and the air. 

In either case allowance must be made for increased 
temperature by equations (10) or (10'). 



26 FUEL 



CHAPTER II 

HEATING POWER OF FUELS 

Thermo-chemistry. — Combustion has been stated to be 
a case of chemical action, and as all chemical change is 
attended with evolution or absorption of heat according to 
perfectly definite laws, these laws must apply equally to 
combustion. A brief consideration of the laws of thermal 
chemistry is essential to a clear understanding of the way in 
which heat is obtained by combustion. 

Unit of Heat. — As all thermo -chemical questions neces- 
sitate the measurement of quantities of heat, it is essential to 
select a unit in which the measurements can be made. The 
unit used for all practical purposes in this country is called 
the British Thermal Unit (B.Th.U.), and is the amount of heat 
required to raise 1 lb. of water 1° F. (from 60° F. to 61° F.). 

The unit used in scientific work is the amount of heat re- 
quired to raise one gramme of water 1° C. (from 0° C. to 1° C), 
or sometimes the amount which is necessary to raise 1 kilo- 
gramme of water 1° C. ; this latter is usually called the 
Calorie. Sometimes also the amount required to raise 1 lb. 
of water 1° C. is taken ; this may be called a Centigrade unit. 
The relationship between these units is easily calculated. 1 

Thermo - chemical Notation. — Any chemical change 
which evolves heat is said to be exothermic and is indicated 
by the sign + , whilst one which absorbs heat is called endo- 
thermic and is indicated by the sign - . The thermal value 
of any reaction is the number of units of heat which would be 

1 (1) To convert a quantity of heat in pound-Centigrade units into the 
corresponding value in B.Th.U. x 1-8. 

(2) To convert a quantity in B.Th.U. into pound-Centigrade units x -5. 

(3) To convert a quantity given in (kilogramme) calories into 
B.Th.U. x 3 968. 

(4) To convert a quantity given in B.Th.U. into (kilogramme) 
calories x -252. 

26 



HEATING POWER OF FUELS 27 

evolved or absorbed by the formation of a molecular weight of 
the resulting compound. If the heat is measured in Centi- 
grade units the weights are taken in grammes ; if in B.Th.U., 
the weights are taken in lbs. The formation of 36-5 lb. 
of hydrochloric acid by the combination of 1 lb. of hydrogen 
with 35-5 lb. of chlorine evolves 39600 British Thermal 
Units, or if the weights be taken in lbs., 22000 lb. Centigrade 
units (C), or if in grammes, 22000 calories. 
This may be written 

H+C^HCl 1 (39600 + ) B.Th.U. (22000 +) C. 

It should not be written, as it often is, H +C1 =HC1 +39600, 
as in that case the equation is incorrect, the two sides not 
balancing. 

Laws of Thermo-chemistry. — There are three import- 
ant laws of thermal chemistry according to which thermal 
and chemical phenomena are connected. 

1. The heat evolved or absorbed in any chemical change is 
fixed and definite, and depends only on the change. It is, 
therefore, independent of any intermediate steps by which the 
change may be brought about ; or to put it in another way, 
it depends only on the initial and final condition. Nernst 2 
states the law : " The energy differences between two 
identical conditions of the system must be the same inde- 
pendently of the way by which the system is transferred 
from one condition to the other." 

According to this law the heat evolution or absorption is 
as much an essential part of any reaction as the mass -change. 
One pound of hydrogen combining with 35-5 lb. of chlorine 
will necessarily form 36-5 lb. of hydrochloric acid, and also 
will necessarily evolve the 39600 B.Th. units of heat. 

In most cases the reaction is not merely the combination 
of two free elements, but is more complex, and in these the 

1 Values in B.Th.U. will be printed in ordinary type, those in gramme- 
Centigrade units in italics, which may be converted into calories by moving 
its point three to the left. 

2 Palmer's translation of Theoretical Chemistry, p. 496. 



28 FUEL 

actual thermal result which can be measured will be the 
algebraic sum of the thermal values of the various parts of 
the reaction, and care must be taken not to overlook any of 
them, or any physical change which may accompany them, 
and which may itself evolve or absorb heat. 

Thus, when hydrogen is made to combine with chlorine in 
solution, the heat of formation is 70770 + B.Th.U., 39320 + C. ; 
but this is made up of two parts : 

Heat of combination of H, Cl . . . 39600 + B.Th.U. 22000 + C. 
Heat of solution of hydrochloric acid in 

water 31170+ 17320 + 



Total . . . 70770+ 39320 + 

When hydrogen and iodine are made to combine, the 
result is still more striking. The two elements in the free 
state can be made to combine only with the greatest diffi- 
culty, their combination being attended with the absorption 
of heat, i.e. the reaction is endothermic. In solution, how- 
ever, they combine readily enough : 

Heat of combination of H, I . . . 10870 - B.Th.U. 6040 - C. 
Heat of solution of hydriodic acid in water 34580 + 19210 + 



Total . . 23710+ 13170 + 

2. " If a chemical change evolves (or absorbs) heat, the 
reverse change will absorb (or evolve) exactly the same quan- 
tity of heat." This is the law of reversibility. 

To use the examples already given : If the formation of a 
pound-molecule of hydrochloric acid evolves 39600 units of 
heat, then to break up the molecule and liberate the elements 
will absorb exactly 39600 units. If the one reaction is 
exothermic, the other must be endothermic to the same 
amount. 

In most reactions there are both combinations and decom- 
positions, and the heat- value of both parts must be taken into 
account in obtaining the final result. If chlorine be brought 
in contact with hydrogen sulphide, decomposition at once 
takes place, and sulphur is separated, H 2 S +2C1 =2HC1 +S. 
The reaction is thus made up of two parts : the formation of 



HEATING POWER OF FUELS 29 

two molecules of hydrochloric acid, and the breaking up of 
one molecule of hydrogen sulphide : 

B.Th.U. C. 

Decomposition of one molecule of hydrogen sulphide . 8530 - 4740 - 
Formation of two molecules of hydrochloric acid . 79200 + 44000 + 



Resultant . . . 70670+ 39260 + 

Had the reaction taken place with a solution of hydrogen 
sulphide, the results would have been a little more complex : 

B.Th.U. c. 
Removal of a molecule of hydrogen sulphide from 

solution 8210- 4560- 

Decomposition of hydrogen sulphide .... 8530 - 4740 - 

Formation of two molecules of hydrochloric acid . 79200 + 44000 + 

Solution of the hydrochloric acid in water . . . 62330 + 34630 + 



Total heat change. . 124790+ 69330 + 

3. Every chemical change effected without the inter- 
vention of extraneous force tends to produce those bodies the 
formation of which will evolve most heat. 

This is called the law of greatest energy, and is of very 
great importance. Hence it follows that reactions which are 
exothermic tend to take place more readily than those which 
are endothermic, and also that bodies which are formed with 
the absorption of heat are usually less stable than those in 
the formation of which heat is evolved. 

Calorific Power. — The calorific power of any substance 
is the heat which is evolved by the union of 1 lb. (or 
gramme) of it with oxygen. It is therefore the thermal value 
of the reaction which takes place divided by the weight of 
the substance taking part in it. 

Combustion of Hydrogen. — The thermal value of the 
reaction 2H +0 =H 2 is 123000 B.Th.U., 68360 C. As this 
is the combustion of 2 lb. (or grammes) of hydrogen, the 
calorific power will be half this, viz. : 

C.P. of H =61500 B.Th.U., 34180 C., 1 
more exactly, 61000 and 33900 liquid water being formed, 

* Thomson's figures, 



30 FUEL 

Combustion of Carbon. — The thermal value of the 
formation of a molecular weight of carbon dioxide from 
carbon and oxygen is C + 20 = C0 2 , 175100 B.Th.U., 97300 C. 
As twelve parts of carbon take part in the reaction, the 
calorific power will be these numbers divided by 12 : 

C.P. of C to (C0 2 ) = 14600 B.Th.U., 8110 C. 

It will be remembered that carbon forms another, a 
lower oxide, carbon monoxide, CO, which contains, for the 
same amount of carbon, one-half the quantity of oxygen. 
What is the heat of formation of this oxide from carbon and 
oxygen ? or, what comes to the same thing, what is the 
calorific power of carbon burning to carbon monoxide ? 
This cannot be determined directly, for, though carbon 
monoxide is readily formed from its elements, they cannot 
be made to combine under conditions suitable for the 
measurement of the heat evolved, but it can be ascertained 
indirectly by taking advantage of the known laws of thermal 
chemistry. 

If twelve parts of carbon be burnt directly to carbon 
dioxide it evolves 175100 B.Th.U., or 97300 C. If twenty- 
eight parts of carbon monoxide (the weight which contains 
twelve parts of carbon) be burnt to carbon dioxide it evolves 
122400 + B.Th.U., or 68000 C, and the heat of formation of 
the carbon monoxide must obviously be the difference 
between the two : 

C+20=C0 2 175100+ B.Th.U. 97300 + C. 

CO + 0=C0 2 122400+ 68000 + 



.\C + 0= 52700+ 29300 + 

which, divided by 12, gives 

C.P. of C to CO =4390 B.Th.U., 2440 C. 

The figures may be stated in another way with the same 
result : 

B.Th.U. C. 

1 lb. carbon burning to carbon dioxide 14600 8110 

2\ lb. carbon monoxide burning to carbon dioxide . . 10210 66 70 

1 lb. of carbon burning to carbon monoxide . . . 4390 2410 



HEATING POWER OF FUELS 31 

It is important to notice that in this case the second 
atom of oxygen combining with the carbon evolves much 
more heat than the first. The probable reason for this is 
that in the free condition the carbon is solid, and in carbon 
monoxide it is gaseous, so that in the formation of carbon 
monoxide the carbon has been vaporized, and the difference 
between the heat evolved by the second atom of oxygen 
and that by the first may be taken as the latent heat of 
vaporization of the carbon, and this, therefore, can be 
calculated from the data given : 

B.Th.U. C. 
Heat evolved by combination of the second portion of 

oxygen with 1 lb. of carbon 10210 56 70 

Heat evolved by combination of the first portion of oxygen 

with 1 lb. of carbon 4390 2440 

Latent heat of vaporization of carbon . . 5820 3230 

Evaporative Power (E.P.). — Engineers very frequently 
use a method of stating the heating power of fuels which 
has the advantage of being independent of any particular 
thermometric scale, and consists in stating the number of 
pounds of water at 212° which would be evaporated by the 
combustion of 1 lb. of the fuel. Since the latent heat of 
vaporization of water is 537 Centigrade or 967 Fahrenheit 
units, the one is easily calculated to the other. 

In the case of carbon, 

(17) &.F.^ 967 - 537 -15 1. 

In the case of hydrogen the relationship is not quite so 
simple, for each pound of hydrogen forms 9 lb. of water, 
which of course must be evaporated ; and as by the condi- 
tions the products of combustion will remain in the gaseous 
condition, the latent heat of steam must be taken into 
account, and 

(18) E.P. of hydrogen - -^- - 9, or ^- - 9 = 54-6. 

Heat of Formation of Compounds. — When a com- 
pound is burned in oxygen or air, the heat evolved is not 



32 FUEL 

the same as would be evolved by the combustion of the 
same weight of the constituent elements in the free condi- 
tion, but may be either greater or less, according as the 
body was formed with absorption or evolution of heat, and 
the difference will be the heat of formation of the body. It 
is easy to see why this must be the case, and, by taking 
advantage of it, it is possible to calculate the heat of forma- 
tion of a compound. For example, what is the heat of 
formation of benzene, C 6 H 6 ? Starting with 6 x 12 =72 lb. 
of carbon and 6x1 lb. of hydrogen, and converting these 
into carbon dioxide and water, the heat evolution must be 
(175100 x 6) + (61500 x 6) = 1420000. (97300 x 6) + (68360 x 3) 
= 789000. 

The formation of six molecules of carbon dioxide and 
three molecules of water from their elements must evolve 
this amount of heat, quite irrespective of the stages through 
which these combining bodies pass, so that, whatever be the 
nature of the changes, the algebraic sum must be 1420000. 
And if heat was evolved when the hydrogen and carbon 
entered into combination to form benzene, when the com- 
pound is burned, the heat of combustion will be less than 
1420000 by the amount of heat evolved in the formation of 
the benzene ; but if the benzene were formed with absorp- 
tion of heat, then when it is burned it will evolve more heat 
than the elements would do in the free condition. 

The heat of combustion of benzene, C 6 H 6 + 150 =6C0 2 + 
3H 2 0, is found to be 1418000 B.Th.U. (788000 C), so that 

B.Th.U. C 

Heat of combustion of benzene 1418000 788000 

Heat of combustion of carbon and hydrogen . . 1420000 789000 



Heat of formation of benzene (approx.) . . . 2000 1000 

So that, if we know the heat of formation of a body and the 
heat of combustion of its constituents, it is possible to calcu- 
late the amount of heat which it will evolve on combustion. 
It will be noted that as heats of formation are calculated 
from differences they do not carry a high degree of accuracy. 



HEATING POWER OF FUELS 33 

Calorific Power of Solid Fuels. — The heat of forma- 
tion of the constituents of solid fuels is quite unknown, and 
therefore it is impossible to calculate exactly the heat of 
combustion of such fuels. It is usual in calculating the 
calorific power of a fuel to assume that the constituents give 
out in burning the same amount of heat that they would do 
if they were in the free condition. This assumption is 
manifestly incorrect, and the results given by it are some- 
times higher and sometimes lower than those determined by 
experiment. Probably no two fuels have identical proxi- 
mate composition, and therefore their heats of formation 
will vary, and may be either positive or negative. As the 
substances used for fuel are usually unstable, their heat of 
formation is small, and the results of these calculations for 
solid fuels are probably not far from the truth — at any rate, 
in most cases ; but it must be remembered that, in the 
present state of knowledge, too implicit confidence must not 
be placed in them. 

In the calculations which follow, c, h, o, s will stand for 
the percentage of carbon, hydrogen, oxygen, and sulphur 
contained in the fuel, and C.P. for the calorific power. 

If the fuel contains no combustible but carbon the calcula- 
tion is very simple. 

(19) C.P. =- X / 4 600 m B.Th.U. 

(19') C.P. = C *jfiQ m C. units. 

If the fuel contains carbon and hydrogen the formula is 
also simple. 

(20) C.P.= cxl4600 1 ^ x61g00 mB.Th.U. 
m cp= cx 8110 +*xMIW f pC 

Since the calorific power of hydrogen is 4-21 times that 
of carbon, these equations may be written : 

(D107) D 



34 FUEL 

. PP ( c +4-21&) x 14600 
( 2l) 0.1^.= m , 

(2n CJ . J.+*gg)x«tt 

Example. — Calculate the calorific power of a fuel containing 70 per 
cent carbon and 30 per cent hydrogen. 

By (lg) c p ^ 70 * 14600 + 30 x61500 = 28670 BThJJ 

or by (180 C.P. J° * <"° f" * Uli0 -1SB60 C. | 

Note. — The highest percentage of hydrogen possible is 25, found in 
methane, CH 4 . 

Most fuels contain oxygen, and this has an important 
effect on the heating power. If the oxygen were free it would 
of course combine with the combustible matter just as the 
oxygen of the air does, and thus evolve heat ; but it is not 
free, it is in combination with some of the other constituents 
of the fuel, and thus these, being oxidized, cannot burn again, 
and so are useless as fuel. The effect of the presence of 
oxygen in a fuel is therefore to render a certain portion of the 
carbon or hydrogen useless for combustion. It is not known 
in what form of combination the oxygen is present, but it is 
assumed to be present in combination with hydrogen in the 
proportions to form water, that is, eight parts of oxygen to 
one of hydrogen, so that the oxygen will render useless J its 
own weight of hydrogen, and the hydrogen which is avail- 
able for combustion will be (h - Jo) ; this therefore is called 
the available hydrogen. The formula for calculating the 
calorific power of a fuel containing hydrogen and oxygen 
therefore is 

(22) C.P. .^jjgg»± ^ fr> * 61500 in B.Th.U„ 
or (22') c .p. = c'x^ + y)x^^ inC ,. 

or, using the form given in equations (21) and (21'), 
{23 ) aR= {c + 4-21(fe^);x 14600 . nBThu 



HEATING POWER OF FUELS 35 

(23 ') C.P.=^ + ^y xmg inC. 

Example. — Find the calorific power of a fuel which contains 50 per 
cent carbon, 26 per cent hydrogen, and 24 per cent oxygen. 
~ „ 50 x 14600+ (26 - V) * 61500 

CR = ioo 

= 730000 + 1415000 = 2145QBThU> 
or CP. J0*Sn0 + W-V)x34180 =11920 Q 

If sulphur be present, then s x 4000 may be added to the 
numerator of the first fraction and s x 2220 to the second. 

Almost all fuels leave on combustion a non-combustible 
residue or ash. This has very little effect on the heating 
power, as it only absorbs a small quantity of heat in being 
heated to the resultant temperature. Similarly, nitrogen 
has no effect, nor has water, since it is assumed that the 
products of combustion are below 212° F. (100° C), so that 
any heat absorbed when the water is converted into steam is 
given up again when it is condensed. 

One inaccuracy in the calculations has been mentioned ; 
there is still another due to uncertainty as to the thermal 
value of carbon burning to carbon dioxide. The figures given 
by Favre and Silberman are : 

Wood charcoal 8080 C. 

Gas retort carbon 8047 ,, 

Native graphite 7762 ,, 

Diamond 7770 „ 

Other investigators obtained values as high as 8140 for wood 
charcoal. 

The value of 8110 may be taken, though it is impossible 
to say in what form the carbon exists in fuels. 

The number 61500 (34180) for the calorific power of 
hydrogen is based on the assumption that the hydrogen is 
gaseous, but in solid fuels it is in the solid condition, and 
therefore heat must be absorbed in melting it. Assuming 
that it combines with oxygen and then melts, the amount 
of heat absorbed would be 9 x 142 in B.Th.U. and 9 x 80 in C. 



36 FUEL 

units, so that the calorific power of hydrogen in solid fuels 
would become : 

(24) C.P. = 61500 - (9 x 142) = 60220 B.Th.U. 
(24') C.P. =34180 -(9x 80) =33460 in C. units. 

As the combined hydrogen is also present in the solid 
condition, the formulae for solid fuels would become : 

(25) C.P. = [c x 14600 + (h- £o) x 61500} -9hx 142 in B.Th.U., 
or (25') C.P. = {cx8U0+(h-\o) x 34180} -9hx80 in C. 

Bodies with Negative Heat of Formation. — Bodies 
which have been formed with absorption of heat give on com- 
bustion more heat than the elements of which they are com- 
posed would do in the free condition, and the decomposition 
of such bodies without combustion will evolve heat. Among 
such may be mentioned acetylene, 86700 -B.Th.U. (48200 - 
C), and carbon disulphide, 46800 -B.Th.U. (26000 -C). 

The influence of the evolution of heat by the dissociation 
of acetylene on the luminosity of flames has already been 
discussed. 

Calorific Power at Higher Temperatures. — The calo- 
rific power has been defined and used in the foregoing 
calculations in the form most convenient for comparison, 
though the conditions are not such as obtain in practice. It 
has been assumed that all the products of combustion are 
cooled below 212° F. ; so that all steam is condensed to water 
and thus gives up its latent heat. In practice this is not the 
case ; the temperature of the products of combustion is 
always above 212°, and therefore the steam remains as such. 
As the heating power which is important for practical 
purposes is that which can be actually obtained, the formula 
can be modified to give this. 

Let the temperature of the products of combustion be 
212° F. (100° C), then the calorific power of hydrogen 
would be : 

(26) C.P. 212 o = 61500 - (967 x 9) = 5280 B.Th.U. 
(26') C.P. 10() ° - 34180 - (537 x 9) =29350 C. 



HEATING POWER OF FUELS 37 

The higher the temperature of the products of combustion 
the less is the effective calorific power, because until the pro- 
ducts of combustion are heated to this temperature, no heat 
can be utilized. The calorific power of hydrogen at t° Fahren- 
heit and t'° Centigrade becomes : 

(27) C.P. t = 61500 - {(967 x 9) + (-4805 x 9 x *)} in B.Th.U. 
(27') C.P., =34180 - {(537 x9) + (-4805 x t x 9)} in C. 

The carbon portion of the equation is not so much affected, 
and the calorific power for carbon at t° F. or t'° C. would 
become : 

(28) C.P. = 14600 - (3-67 x .2090, 

(28') C.P. =8110 - (3-67 x -209 f), 
and a fuel containing carbon, hydrogen, and oxygen : 

(29) C.P. = 

[(c x 14600) - 367c x -209 X t] + 61500(ft - £o) - (9C7 x 9h) +(-4805 x 9h x I) in B Th jj 

or (29') C.P. = 

(c X 8110) - (3-67c X '909 X t)+3U180(h - jo) - (537 X 9h)+(-h805 X 9h X C.) . c 
100 

In the above 0-4805 and 0-209 are the specific heats per 
unit weight of H 2 and C0 2 respectively. The formulae do 
not apply at high temperatures because of the large increase 
in the specific heats. 

Calorific Intensity (C.I.). — It is often not sufficient to 
know the actual heating power of a fuel, but it is required to 
know also the temperature which could be obtained by burn- 
ing it, or, as it is called, the calorific intensity or pyrometric 
heating effect. The pyrometric effect and the absolute heat- 
ing power are not identical or even proportional. It is 
obviously impossible to calculate a temperature attainable 
under any practicable conditions, since all the circumstances 
are too variable ; but it is easy to calculate it under certain 
assumed conditions, which, though not attainable in practice, 
allow of the ready comparison of the heating power of various 
fuels. The calorific intensity may be defined as the rise of 
temperature which would be produced if 1 lb. (or gramme) 



38 FUEL 

of the fuel were burnt in exactly the right quantity of oxygen 
under such conditions that combustion was perfect and there 
was no loss of heat. 

The temperature would depend on the amount of heat 
liberated and on the nature and weight of the products of 
combustion which have to be heated. The products of com- 
bustion can readily be reduced to a water equivalent, i.e. a 
weight of water which would require the same amount of heat 
to raise it one degree. The water equivalent will always be 
W x S, where W is the weight of the product of combustion, 
and S its specific heat ; and if C.P. be the amount of heat 
evolved, then T, the rise of temperature, will be : 

C.P. 



(30) T = 



WxS' 



If 1 lb. of carbon at 32° F. (0°C.) be burned in 2-67 lb. 
of oxygen it will form 3-67 lb. of carbon dioxide, which has 
a specific heat of -209 ; so that 

14600 14600 iq(un o F 

(31) 0J * = 3*7^209 ~ Wf =1904 ° F ' 

This is a rise of temperature, so that if, at starting, all 
the substances were at 32° the final temperature would be 
19070° F. 

In Centigrade degrees the figures would be : 

(31') C.I.c. = 3 . 67 x %m = 7m =10570° C. 

The case of hydrogen is a little more complex. The heat 
evolution is 61500 B.Th.U., which has to be distributed over 
9 lb. of steam produced by the combustion, having a specific 
heat of *4805 ; but the 9 lb. of water has to be converted into 
steam, which will absorb 966 x 9 units of heat, and thus 
reduce the heating power by that amount. But during the 
180°, i.e. from 32° to 212°, the specific heat is not -4805, but 1; 
so the difference must also be deducted, and the formula for 
the calorific intensity of hydrogen becomes : 



(32) C.I.f. = 



HEATING POWER OF FUELS 39 

61500 - {967 + (1 - -4805)180}9 



9 x -4805 
51970 



4-3245 



= 12020. 



This is a rise of temperature, so that the temperature of pro- 
ducts of combustion would be 12020+32 = 12050° F. 
In Centigrade degrees : 

34180 -{537 +(1-.4805)100}9 
(32) C.l. c .= g x m4805 -00W. 

These formulae can readily be applied to fuels containing the 
ordinary constituents. 

c x 14600 + (h - |o)61500 - ^967 +(1 - -4805)180 x (9ft +w)} 
{3d) UI.f.- (3-67cx-209+(9fc+u;) x -4805)100 

ex 8110 +(h- \o)34180 - {537 + {1- -4805)100 x(9h+ w)} 
{3d) UL- (3-67cx -209 +(9h+w)x -4805)100 

where, in addition to the symbols used above, w is the 
quantity of moisture in 1 lb. of the fuel. To obtain the 
resulting temperature the figure obtained for the calorific 
intensity must be added to the temperature at which 
combustion takes place. To calculate the pyrometric 
heating power, using air in place of oxygen, 

77 
(34) { 2-67c + 8(fc - \o) } x — x -248 must be added to the 

denominator of the fraction, and if there be an excess of 
air e, then e x -241 must also be added. 

The figures obtained by these formulas are not results 
which would actually be obtained, because the specific heats 
of the various products of combustion are not constant but 
increase rapidly as the temperature rises. 

Comparison of Hydrogen and Carbon. — The calorific 
power and intensity of fuels are related, but they are not 
identical or proportional, as will be seen from the following 
tabular statement from Watts' Dictionary : 



40 



FUEL 





■a 


0) ►*> o 


1 




6 


Heat Units. 


.2 


Thermal Effect. 


6 

"-3 






£* 






























C°. 


F°. 




Carbon . 


1 


2-67 


1 


3-67 


l 


8080 


14544 


l 


10174 


18297 


1 


Hydrogen 


1 


8 


3 


9 


2-4 


34180 


61524 


4-265 


6743 


12021 


•681 



Other Formulae. — Many other formulae for calculating 
calorific power have been suggested. That of M. Cornu is 
very frequently used ; it is 

8080 C +11370 C" +34180 H 



C.P. 



100 



where C is the percentage of fixed carbon, C" the percentage 
of volatile carbon, and H the percentage of hydrogen in the 
fuel, and the results are given in Centigrade units. 

This equation is readily modified to give the result in 
British units ; it then becomes 

14544 C +20390 C" +61524 H 



C.P.= 



100 



the symbols having the same meaning as above. 

The formulae based on the calorific power of the elements 
necessitate for their use a knowledge of the ultimate composi- 
tion of the fuel, and as this can only be obtained by a trouble- 
some combustion analysis of the fuel, attempts have been 
made to devise formulae which can be used with simpler data. 

Of these, that due to O. Gmelin is probably the best ; it 
is C.P. =[100 - (w +a)]80 -c x 6w, 

where w is the percentage of water, a the percentage of ash, 
and c a constant varying with the amount of water. The 
result is given in calories. 

The value of c is, for coals with — 

Percentage of Water 



c = 
4 
6 

12 

10 



(1) Less than 3 per cent 

(2) Between 3 and 4-5 

(3) „ 4-5 „ 8-5 

(4) „ 8-5 „ 12 

This formula seems to give good results with many coals. 



(5) Between 12 and 20 per cent 8 

(6) „ 20 „ 28 . .6 

(7) Over 28 per cent . . 4 



FUELS— WOOD, PEAT, COAL 41 

It has been suggested by Welter that the heat evolved 
by a fuel when burned is proportional to the amount of 
oxygen with which it combines, and on this assumption 
(often called Welter's law) attempts have been made to 
estimate the heating power of a fuel by finding the amount 
of oxygen with which it will combine. The law is probably 
nearly correct where there is no change of state or chemical 
change except combination ; but as in all solid fuels the 
solid carbon is converted into the gaseous form, the law 
breaks down and is of no practical use. 

The amount of heat evolved per unit of oxygen taken 
up is : 

(1) By combustion of hydrogen . . 7690 B.Th.U. 4270 C. 

(2) „ solid carbon | ^ 

to carbon dioxide J 



CHAPTER III 

FUELS — WOOD, PEAT, COAL 

Nature of Fuels. — All fuels in common use consist 
mainly of carbon and hydrogen, and all, with perhaps the 
exception of mineral oils and natural gas, are of vegetable 
origin. 

Classification of Fuels. — The following classification 
of fuels will answer every purpose : 

I. Solid fuels. 

(a) Natural. 

(1) Wood. 

(2) Peat. 

(3) Coal. 
(6) Prepared. 

(1) Charcoal. 

(2) Peat charcoal. 

(3) Coke. 

(4) Briquettes. 



42 FUEL 

II. Liquid fuel. 

(a) Natural. 

Natural oils. 

(6) Prepared. 

Distilled oils. 

III. Gaseous fuel. 

(a) Natural. 

Natural gas. 

(6) Prepared. 

(1) Coal-gas. 

(2) Producer-gas. 

(3) Water-gas. 

(4) Oil-gas. 

Wood. — Wood may be regarded as the natural fuel of 
man : certainly it was the first, and for very many ages the 
only one, with which he was acquainted. It is still used in 
some minor operations, but has been abandoned for all 
metallurgical processes, except in regions where other forms 
of fuel are dear or unobtainable. 

Wood is the more or less hardened vegetable tissue of 
trees. The stems and larger branches are called simply 
wood, while the smaller branches and all the wood of bushes 
and small trees is known as brushwood. 

In the early days of its growth every plant is soft and 
herbaceous, but in time, in the case of those that live several 
years, the soft cells and tissues become hardened or filled up 
by the deposition of woody matter, thus converting the 
herbaceous plant into wood. As the plant grows, the older 
cells become more and more filled up, till after a time they 
cease to perform their functions, and may even decay with- 
out impairing the vitality of the tree. The hard centre of 
the tree is often called " heart- wood," whilst the younger 
and outer portion is " green or sap wood." Under the bark 
there is a layer of living and growing cells, by means of 
which fresh wood is formed and the tree increases in size. 



FUELS— WOOD, PEAT, COAL 



43 



The principal constituent of wood is cellulose — a sub- 
stance which is seen very nearly pure in white cotton fibre 
— which has the formula C 6 H 10 O 5 , and contains 44-42 per 
cent carbon, 6-22 per cent hydrogen, and 49-36 per cent 
oxygen ; the composition being the same whatever is the 
nature of the plant from which it is taken. 

Composition of Wood. — The materials deposited in the 
cells as the tree grows vary in composition, but on the whole 
they are richer in carbon and hydrogen than cellulose, so 
that though pure cellulose contains no available hydrogen, 
wood always contains a small quantity. 

The following analyses will give a sufficient idea of the 
composition of wood. The figures in the first column may 
be taken as an average ; those in the other three columns 
are actual analyses, and are taken from Percy's Metallurgy, 
vol. i. (C, H, O, and N are calculated on an ash-free basis.) 





Average. 


Oak, 
120 years. 


Birch, 
60 years. 


Willow. 


Carbon .... 

Hydrogen 

Oxygen 

Nitrogen 

Ash .... 


51 
6 

42 
1 
2 


50-97 
6-02 

41-96 
1-27 
1-93 


50-59 
6-21 

4216 
101 
210 


51-75 
619 

4106 

•98 

3-67 



Some plants and parts of plants are exceptionally rich in 
carbon and hydrogen, as, for instance, the spores of club- 
moss, which contain about : 

Carbon 61-5 

Hydrogen ...... 8-4 

Oxygen and nitrogen . . . . .27-7 

Ash 2-4 

Water in Wood. — Wood always contains a considerable 
quantity of water. In the growing condition the cells and 
vessels are filled with the sap fluids on the circulation of 
which the growth of the plant depends. Freshly felled 
wood contains 50 per cent or more of water — the amount 
varying with the kind of tree, the part of the tree, the age, 
and the season of felling. The young wood, branches, and 



44 



FUEL 



leaves contain more than the stem ; and the older the wood 
the less water it usually contains. The amount is greatest 
in spring, when growth is active, and least in winter. When 
a tree is felled and exposed to the air it loses water, and as 
the bark hinders drying it is usually removed, or the tree is 
" barked." After a few weeks' exposure, under cover, it 
loses as much water as it will do under the circumstances, 
and in this condition it is said to be " air-dried," but still 
retains 15 to 25 per cent of moisture. The following may 



be taken as the average compos 

Carbon 

Hydrogen 

Oxygen 

Nitrogen 

Ash . 

Moisture 



tion of air-dried wood 

40 
4-8 

32-8 

•8 

1-6 

20-0 



1000 



Distillation of Wood. — When wood is heated in a 
closed vessel water and volatile matters are expelled, and a 
residue of charcoal is left, which consists of pure carbon and 
ash. 

The following may be taken as an average result : 

Volatile . . . . . . .73 per cent. 

Charcoal ....... 27 „ 

Fixed carbon . . . . . 25 „ 

Ash 2 

Ash of Wood. — The ash which is left in burning away 
all the combustible portion of wood consists of the inorganic 
matters which were present. These constituents are not 
accidental, but are a necessary part of the plant ; each plant 
containing the ash constituents in more or less definite pro- 
portions. The constituents of the ash are principally in the 
form of oxides and carbonates, depending to some extent on 
the temperature at which the wood was burned. This gives 
no clue to the way in which the elements were combined in 
the wood, since all organic compounds of the metals give 
oxides or carbonates on combustion. The ash is usually 
white, and consists chiefly of carbonates of potash and lime, 



FUELS— WOOD, PEAT, COAL 



45 



with smaller quantities of soda, magnesia, oxide of iron, 
alumina, and silica, the amount of the last named varying 
much with the nature of the plant. The composition of 
wood ash is of no metallurgical importance. 

Specific Gravity of Wood. — Wood floats on water, and 
bulk for bulk is therefore lighter. This is due to the fact 
that wood is very porous, and that the spaces are filled with 
air. If the air be removed and replaced by water, as when 
the wood becomes water-logged by long soaking, then the 
wood becomes heavier than water and sinks. The specific 
gravity of wood including the air-spaces varies from -54 to 
over 1. Excluding air-spaces the specific gravity is about 
1-6. 

Wood as a Fuel. — Wood is not a good fuel. When 
air-dried it contains a large quantity of water, which has to 
be evaporated by the heat of combustion. It contains a 
large quantity of combined, but very little available hydro- 
gen, so that its calorific power is low. Dry wood has only a 
calorific power of about 7000 B.Th.U., and when air-dried 
only about 5600 B.Th.U. The calorific intensity is also low. 

Many attempts have been made to estimate the relative 
value of the various woods as fuel. The figures given by 
O. Pictet are : 



Lime (taken as unity) 
Scotch fir, elm, aspen 
Willow, horse-chestnut, larch 
Maple .... 
Black poplar 

Alder, birch, hornbeam, oak 
Ash 



•98 
•97 
•96 
•95 
•94 
•92 



The heating power of the soft woods is therefore as great as 
that of the harder woods. 

Wood is very light and bulky ; it kindles easily, and burns 
with a long, luminous, often smoky flame. Long soaking in 
water seems to diminish the specific gravity and heating 
power of the wood, but there is little, if any, difference 
detectable in the composition. 

Any vegetable matter that is sufficiently abundant and 



46 FUEL 

cheap may be used as a fuel under suitable conditions. 
Spent tan, straw, and many other substances have been 
successfully used. Dry straw has a calorific power of about 
6300 B.Th.U. 

Peat. — Under certain conditions of moisture and tempera- 
ture, various low forms of vegetable life flourish luxuriantly, 
and as they die down their remains accumulate faster than 
they decay, so that each generation helps to form the soil on 
which the next generation grows. In this way there gradu- 
ally collects a mass of decaying vegetable matter, which may 
accumulate to a great thickness, forming beds of peat. 
These peat-mosses or peat-bogs are produced mainly in moist 
districts in temperate climates, sometimes occupying low- 
lying river- valleys, at others depressions in table-lands or 
among hills. 

In this country the peat is composed almost entirely of the 
remains of mosses, those of the genus Sphagnum being far 
the most abundant. But in other countries these are some- 
times quite absent, and therefore the peat is made up of the 
remains of other forms of plants. 

As the plant-remains accumulate by growth and decay, 
it follows that the most recent peat must be at the top and 
the oldest at the bottom. The top layers will consist of the 
tangled roots and stems of the plants, only slightly decayed, 
so that the separate plants can be distinctly made out. It is 
usually light-brown in colour and of low specific gravity. 
Lower down it will be darker in colour and denser, the 
separate plants being less readily distinguishable, and at 
the greatest depth it may have passed into a nearly black, 
compact mass, in which all trace of the separate plants of 
which it is composed is lost. 

Owing to the way in which the peat has been formed, it 
is usually very wet, often containing, when freshly got, as 
much as 80 per cent of moisture, and even after thorough 
air-drying it will usually contain 20 per cent. 

Composition of Peat. — The following analyses of peat, 
from Percy's Metallurgy, may be taken as examples, but it 



FUELS— WOOD, PEAT, COAL 



47 



must be remembered that samples from different beds in the 
same district, or even from different parts of the same bed, 
may vary so very much in composition that it is quite 
impossible to give anything like an average composition : 





Kilbeggan. 


Devonshire. 


Philipstown, 
Ireland. 


Abbeville, 
France. 


Carbon .... 

Hydrogen 

Oxygen 

Nitrogen 

Ash .... 


6104 
607 

| 30-46 | 
1-83 


54-02 
5-21 

28-18 
2-30 
9-73 


57-53 
6-83 

32-23 
1-42 
1-99 


5703 
5-63 

29-55 
2-21 
5-58 



A sample of Wicklow peat (dry) gave : 

Volatile . 71-6 

Coke 28-4 

Fixed carbon ...... 27-17 

Ash 1-23 

Ash of Peat. — The amount of ash from peat is often very 
large ; the tangled mass of roots and stems acts as an 
efficient filter, and retains much of the solid matter which 
the water carries in suspension. The ash, therefore, consists 
in many cases only to a very small extent of the remains of 
the inorganic matter in the plants from which the peat was 
formed, and its composition is different from that of wood. 
Alkalies are usually lower, and oxide of iron and earthy 
materials are much higher in amount ; sulphates are often 
present in considerable quantity ; and sometimes metallic 
compounds in such quantity as to be of value for the 
extraction of the metal they contain. Peat is often so 
impregnated with iron as to constitute a bog-iron ore ; in 
Anglesea some of the peat contains so much copper that 
the ash yields about three per cent of the metal ; while in 
other cases considerable quantities of iron pyrites have 
been found. 

Density of Peat. — Peat varies much in density. It 
may be as light as -25 or as heavy as 1*4 According to Sir 
Robert Kane : 



48 FUEL 

1 cubic yard of light peat (as used for domestic burning) 

weighs ......... 500 lb. 

1 cubic yard of good peat weighs ..... 900 „ 

1 „ „ densest „ ..... 1100 „ 

Cutting and Preparing Peat. — For domestic use, where 
peat is employed as fuel, it usually undergoes no preparation 
except air-drying. It is cut from the moss by means of hand 
cutters in rectangular blocks, and these are allowed to dry 
in the air under cover till they are dry enough for use. Many 
attempts have been made to prepare a good fuel for manu- 
facturing purposes from peat, but hitherto without much 
success. With this object the peat is first cut either by hand 
or, better, by machinery — of which many kinds have been 
devised ; it is then usually shredded or pulped, stones, pieces 
of wood, and anything else which will not pulp being separ- 
ated, and the pulp is pressed into blocks under great pressure 
— these being often perforated to allow escape of moisture — 
and dried at a moderate temperature in air or superheated 
steam. As a rule, when fuel of fair quality has thus been 
made, the cost has been too great to allow it to come into 
extended use. 

Peat as Fuel. — Peat is not a good fuel. It contains too 
much water, usually too much ash — and this generally of an 
objectionable kind. It contains very little available hydro- 
gen, and has a very low calorific power, about 5000 B.Th.U. 
or less, and its calorific intensity is also low. The evapora- 
tive power of dry peat may be taken as about 5-5, that of 
peat in its ordinary condition as 4-5, so that weight for weight 
its heating power is not more than half that of coal, whilst 
bulk for bulk it is much less. Peat has, therefore, all the 
defects of wood with the addition of the high ash, and as it 
burns it crumbles down, the residue or coke having no 
cohesive power whatever. The pressed blocks also have 
this defect, and are usually so soft that they will not bear 
handling. 

Coal. — This is by far the most important fuel, and prac- 
tically all the energy required for metallurgical and manu- 



FUELS— WOOD, PEAT, COAL 49 

facturing purposes is obtained directly or indirectly by its 
combustion, except in the localities where natural gas or oil 
is available. Common and well known as coal is, it is 
extremely difficult if not impossible to give a satisfactory 
definition ; that is, one which, while including all varieties 
of coal, shall exclude all other substances. This was well 
shown in the Torbanehill case tried in Edinburgh in 1853, 
with the object of determining whether a certain mineral, 
torbanite or Torbanehill mineral, was or was not a coal. 
It was only after a lengthy trial, in which a great number 
of scientific witnesses were examined on both sides, that the 
substance in question was decided to be a coal. 

The best definition of coal which has yet been framed 
is that due to Dr. Percy : " Coal is a solid stratified 
mineral substance, black or brown in colour, and of such 
a nature that it can be economically burned in furnaces or 
grates." 

Exception may be taken to this because it makes the 
definition of coal depend on whether it can be economically 
used or not, and therefore to some extent on the nature of 
the grate ; but it must be remembered that for practical 
purposes coal is only required for burning, and therefore the 
definition is quite sufficiently accurate. 

Another definition which has been suggested is, " any 
mineral substance used as fuel which is mainly made up of 
the remains of plants." 

Geology of Coal. — Coal is made up almost entirely of 
matter derived from plants. The plants lived in an age very 
much more remote than that in which the oldest peat was 
formed, and therefore their remains have undergone very 
much greater changes in composition and physical properties. 
So great has been the transformation, indeed, that composi- 
tion alone would not be sufficient to prove the vegetable 
origin of coal. All the ordinary coals were formed in situ, 
the plants living and dying on the spots where the coal 
produced from them is now found. During the period when 
the British coal-measures were being formed, the whole of 

(D107) B 



50 FUEL 

central England, Wales, Ireland, part of Scotland, and part 
of the south of England, was covered with vast forests, 
was indeed probably made up of " broad swampy tree- 
covered flats," on which flourished a most luxuriant vegeta- 
tion consisting not only of small plants like those of peat- 
mosses, but also of large trees, all, however, belonging to 
comparatively low forms of vegetable life allied to the living 
ferns, mosses, club-mosses, and horse-tails. Here the plants 
lived, shed their leaves and spores, and ultimately died ; a 
mass of vegetable matter thus accumulating, and in time 
acquiring great thickness. The dead vegetable matter gradu- 
ally underwent decay, the less stable portions going first, 
and those more stable — such as the bark and spores — 
resisting the decomposing agencies more powerfully. Gradu- 
ally and very slowly the land then subsided, and at last the 
sea washed up over the morass, depositing layers of mud 
which afterwards became hardened into shale and sandstone. 
So gradually did this change take place that the soft mass 
of vegetable matter was not disturbed, many of the tree- 
stumps remaining standing, and becoming embedded in the 
mud to be afterwards replaced by stone, the cast retaining 
the form of the tree. After the lapse of further ages the 
land ceased to sink, and again began to rise, the deposit 
became once more surface, trees sprang up, sending their 
roots down into the underclay and their stems up into the 
air, and once more an accumulation of vegetable matter 
commenced. In many instances this alternation was 
repeated a large number of times, giving rise to many layers 
of vegetable matter separated by beds of shale or sandstone, 
or in some cases, where the submergence had been greater, 
even limestone. In some places the land condition was 
more permanent than in others, and here beds of coal of 
greater thickness accumulated. 

As to the time taken by the formation of these deposits 
it is impossible to form even the vaguest conception — it was 
a very long time, and that is all that can be said. In some 
cases the thickness of a bed of coal representing a distinct 



FUELS— WOOD, PEAT, COAL 51 

period of growth may be less than an inch, in others it may 
be many yards ; so also the interbedded shales, etc., may 
be very thin or may attain great thickness. 

After the formation of our chief coal-beds conditions 
underwent a more permanent change ; the land sank again 
beneath the sea, and the regions where the luxuriant vegeta- 
tion of the coal forests had nourished became sea-bottom, 
upon which beds of limestone, sandstone, etc., were deposited. 
Then other changes took place. The rocks were upheaved 
and broken, parts being thrown above the surface of the 
sea. Denudation at once commenced by the action of water 
and air, the rocks exposed were washed away and carried 
into the sea, the remains of them helping to form fresh beds. 
Thus what had before been continuous deposits became 
broken up into the series of isolated coal basins as we have 
them now, though in many cases they have afterwards been 
covered by other deposits. The arrangement of the deposits 
is not the same in all localities. " The remarkable small 
scattered coal basins of France and central Germany were 
probably, from the first, isolated areas of deposit, though 
they have suffered, in some cases very greatly, from subse- 
quent plication and denudation. In Russia, and still more 
in China and western North America, carboniferous rocks 
cover thousands of square miles in horizontal or only very 
gently undulating sheets." x 

It must not be supposed that all coal is of exactly the 
same age, or that the conditions of its deposition were in 
operation at all places at the same time. When, for instance, 
much of England and Ireland was at the bottom of the sea 
during the carboniferous limestone period, coal-beds were 
being formed in Lanarkshire. 

There is another variety of coal formed at about the 
same period as the ordinary coal, the origin of which is 
slightly different. This is the cannel coal, which consists 
of coaly matter often more or less intimately mixed with 
clay or shale. This coal " always occurs in basin-shaped 

1 Geikie, Text-book of Geology, p. 804. 



52 FUEL 

patches thinning away to nothing on all sides," x and fre- 
quently merging into mere carboniferous shale, and often con- 
taining fossil fishes. Cannel coal has probably been formed 
from vegetable matter drifted down the streams into ponds 
or lakes ; this matter being mixed with other sediment, and 
ultimately undergoing decay till it was reduced to the condi- 
tion of mere pulp. As the mud would tend to deposit first, 
near the mouths of the streams these would be carbonaceous 
shales ; and, as the distance increased, the substances held 
in suspension by the water would gradually contain less 
mud and more vegetable matter, till ultimately the former 
would cease and the deposit become a mass of vegetable pulp. 

Coal-beds occur in various parts of the world, and, though 
as indicated above they are of various geological ages, they 
all belong to a very remote past. Wherever in any place 
there was a very luxuriant vegetation for a long period, 
followed by a time of depression, during which the sea 
flowed over the land and by depositing mud protected the 
vegetable matter from complete decay, beds of coaly matter 
might be formed. Some beds belong to very much more 
recent periods than the true coals. 

Structure of Coal. — The vegetable matter of which coal 
is composed has undergone such complete mineralization 
that by the eye no trace of its vegetable structure can be 
seen. If ordinary coal be examined it is found " that it 
splits most easily in three directions nearly at right angles 
to one another, so that it comes away in rude cubical masses. 
Two of these planes are roughly at right angles to the planes 
of bedding of the rocks among which the coal occurs. The 
faces of the block on these sides are smooth and shining, 
and do not soil the fingers. One of the faces called the bord 
or cleat is very marked, the other called the end is less 
sharply defined. The third direction in which the coal 
naturally breaks is parallel to the bedding of the rocks 
above and beneath it ; the planes of division in this direc- 
tion are dull and greasy to the touch, owing to a thin layer 

J Ooal, edited by Prof. Thorpe, p. 30. 



FUELS— WOOD, PEAT, COAL 53 

or numerous patches of a dark black sooty substance which 
looks like charcoal, and is called mineral charcoal or mother 
of coal." 1 

" Thus coal may be said, speaking broadly, to be com- 
posed of two constituents : firstly mineral charcoal, and 
secondly coal proper. The nature of the mineral charcoal has 
long since been determined. Its structure shows it to consist 
of the remains of stems and leaves of plants reduced to a little 
more than their carbon. Again, some of the coal is made up 
of the crushed and flattened bark or outer coat of the stems of 
plants, the inner wood of which has completely decayed 
away." 2 A considerable proportion of the coal is made up of 
material, vegetable, it is true, but certainly not the remains 
of the stems or leaves of plants, and it is now pretty clearly 
made out that it is composed of the remains of a vast number 
of spores of a plant allied to the Lepidodendron. It must be 
remembered that the great trees of the coal period all belonged 
to the cryptogams or non-flowering plants which are pro- 
pagated by means of spores. 

When ordinary coal is ground into plates so thin that they 
become translucent and these are examined by means of a 
microscope by transmitted light, the coal is found to be com- 
posed of two parts, a yellowish translucent mass and a dark 
opaque mass, and the yellowish mass is seen to be made up 
of small sac -like bodies which are the spores. Many coals 
seem to be almost entirely made up of spores, sometimes 
contained in sporangia, and the opaque matter is probably 
to a large extent also masses of spores which have undergone 
further mineralization. Coals which burn with a flame 
usually contain a large amount of spore matter. Spores of 
cryptogamous plants are of a very highly resinous nature, 
and therefore would probably resist the decomposing action 
of water and air far better than ordinary wood, and they 
contain a large amount of free hydrogen, and thus would be 
likely to burn with a flame. 

1 Coal, edited by Prof. Thorpe, p. 17. 
8 Huxley, Collected Works, vol. viii. p, 141. 



54 FUEL 

As metamorphosis goes on, the coal changes its character, 
the quantity of black opaque matter increases until in anthra- 
cite this is in such large proportion that it is impossible to get 
a translucent section at all. The black matter is probably 
only altered spore-matter, though Prof. Williamson regards 
it as altered " mother of coal." 

" Professor Huxley states that all the coals he has ex- 
amined agree more or less closely in this ultimate structure, 
spores are always present, and in the best and purest coals 
they make up nearly the whole of the mass, and he accounts 
very satisfactorily for the preservation of this part only of the 
plants on the ground that the resinous nature of the spores 
protected them from decay ; while the wood rotted away, 
the bark, which is rather less destructible, was the only part 
of the stem which escaped, and thus appears in the mother 
of coal." x 

Principal Dawson has pointed out that most of the coals 
of Canada are not composed mainly of spores, but of bark and 
other woody material. 

Some carbonaceous shales seem to contain spores in 
abundance. 

Distribution of Coal. — Coal is very widely distributed over 
the world. Fig. 3 shows, as far as is known, the relative quan- 
tities of coal available in different countries. It is of course 
only a very rough approximation. The world's total avail- 
able coal of all kinds is estimated at 7,300,000 million tons, 
or about 6000 times the present total annual consumption. 

Classification of Coals. — Coals may be classified in 
various ways. The following is convenient : 

Lignite or Brown Coal. 
Bituminous or True Coals. 
Anthracite. 
Cannel Coal. 

Lignite or Brown Coal. — This variety of coal is of more 
recent age than the true coal, occurring in rocks of tertiary 

1 Coal, p. 23. 



FUELS— WOOD, PEAT, COAL 



55 



age, and it is therefore, as might be expected, intermediate in 
composition between wood and coal. It is very widely dis- 
tributed over Europe, the most important deposits being 
those in Bohemia, and as since their formation the rocks 
have undergone comparatively little disturbance, they do not 
lie in basins like true coal. There is only one British deposit, 





BbodB 

Fig. 3. — Coal available (pre-war) in different Countries. 

1. United States 52 per cent. 

2. Canada 16* 

3. China 13J 

4. Germany . 5$ ,, 

5. Great Britain 2J 

6. Siberia 2J 

7. Australia 2J 

8. Russia | 

9. France, Belgium, etc 4J „ 

100 

that of Bovey-Tracey in Devonshire, which is probably of 
oligocene age. 

There are several varieties of lignite. 

Bituminous coal has a brown colour, and shows its woody 
structure very distinctly, whence it is often called wood-coal. 

Brown coal or lignite proper is harder and more compact, 
shows the woody structure less distinctly, and has a brown 
colour. 

Pitch coal is brownish-black or black in colour, breaks 
with a conchoidal pitch-like fracture, may be dull or shiny, 
and shows no woody structure. 

Freshly got lignite often contains a large quantity of 
water, and some samples are very high in ash. The following 
analysis of Bovey lignite given by Dr. Percy may be taken as 
a type : 



56 



FUEL 



Carbon 
Hydrogen 
Oxygen 
Ash 



Bovey. 


Average. 


66-31 


68 


5-63 


5-5 


22-86 


26-5 


2-27 


20 



Examples of Lignites 





1. 


2. 


3. 


4. 


Volatile matter . 


54-02 


48-30 


45-6 


40-2 


Coke .... 


45-98 


51-70 


54-4 


59-8 


Fixed carbon 


36-08 


50-47 


41-86 


51-6 


Ash .... 


9-9 


1-23 


12-54 


8-2 


Sulphur 




. . 


312 




Moisture 




24-64 




1-21 



1, Bovey. % Pitch coal, Servia (J. I. and S. I.), 
(cretaceous age), Klose. 



3, Austria (Schrotter). 4, Colorado 



Lignite kindles easily, burns with a long smoky flame, and 
has a low calorific power. If the powder be heated it does 
not cake. 

Lignite is very little used for metallurgical purposes, 
except in districts where no other fuel is available. 

Bituminous Coals. — Bituminous coals burn with a 
yellow luminous smoky flame resembling that of the mineral 
bitumen, whence the name. They are mostly black in colour, 
though some are brown, and they mostly soil the fingers. All 
bituminous coals of Great Britain belong to the carboniferous 
period. 

When a powdered coal is heated in a closed crucible or 
retort gaseous and liquid products of destructive distillation 
are given off, and a solid residue of coke is left. According to 
the nature of this coke coals are divided into two great groups : 

1. Caking Coal. — Some coals when heated soften, appear 
to fuse, and the particles become aggregated into a continuous 
mass, so that the residual coke is hard, compact, and shows 
no trace of the original coal particles. If such a coal be 
charged into a retort in lumps, the lumps will fuse together 
and yield a solid coherent mass. 

2. Non-caking Coal. — With the extreme varieties of this 



FUELS- WOOD, PEAT, COAL 57 

class the coals undergo little apparent change on heating. 
They do not soften or fuse, and if the coal be powdered the 
particles do not cohere, but the coke is a powder. In less 
extreme cases the particles cohere, but the mass does not 
swell up as a caking coal does, and the coke is soft and friable. 
If such coals be coked in lumps the pieces of coke retain 
the form of the coal, and if they cohere at all it is only 
slightly. 

There is every gradation between caking and non-caking 
coals, so that in many cases it is impossible to say where one 
ends and the other begins, but a coal is not usually spoken of 
as a caking coal unless it yields a fairly hard and coherent 
coke. 

Cause of Caking. — On what the property of caking 
depends has not yet been thoroughly made out. No doubt it 
is on the chemical composition, but certainly not merely on 
the relative quantities of carbon, hydrogen, oxygen, etc., 
which the coal contains, for two coals may have the same 
ultimate composition and yet one may cake and the other 
not. 

There are two classes of coal which do not cake — those 
poor in oxygen and rich in carbon, approaching therefore to 
the anthracites, and those rich in oxygen and poor in carbon, 
which approach more nearly to the lignites. As examples the 
following analyses given by Dr. Percy may be quoted : 





Non-caking, poor 




Non-caking, ri 




in oxygen. 


Caking. 


in oxygen. 




Dowlais. 


Northumberland. S. Stafford. 


Carbon 


89 


78-65 


7612 


Hydrogen 


4-43 


4-65 


4-83 


Oxygen . 


4-82 


13-66 


15-72 


Nitrogen 


•55 


•55 


100 


Ash ... 


1-20 


2-49 


2-33 



These figures do not seem to indicate any except the most 
general relationship between the composition and the caking 
property. Ash, sulphur, and nitrogen vary much in coals, 
and as they may vary between very wide limits without in 
any way affecting the caking properties, they may be left 



58 



FUEL 



out of account. In order to get at the relationship existing 
between the three essential elements the analyses should be 
written in such a way that the others do not interfere with 
the result. This may be done, as also suggested by Dr. Percy, 
by calculating, not the percentage of the whole mass, but the 
quantities combined with 100 parts of carbon. Written thus 
the three coals would give — 

1. 2. 3. 

Carbon . . . . .100 100 100 

Hydrogen . . . 4-98 5-90 6-35 

Oxygen .... 5-42 17-37 21-97 

Dr. Percy suggested as a generalization from a large 
number of experiments and analyses that when the quantity 
of oxygen, stated as above, as a percentage of the carbon 
present, fell between 8 and 18, the coal would cake, whilst if 
it were lower or higher it would not. 

This cannot be taken as an absolute rule, for there are 
many exceptions to it, but it holds good in a very large 
number of cases. 

Classification of Bituminous Coals. — Many attempts 
have been made to form a good classification of bituminous 
coals, but owing to the great variety among them, and to the 
fact that many of their properties seem to vary independently 
of the rest, no very satisfactory classification is possible. 
That due to Griiner is probably the best which has been 
proposed, and answers very well for practical purposes. 
Griiner' s names for the classes are not in harmony with those 
in general use in this country, so it will probably be most 
convenient to translate them into their equivalents — 






Griiner's Names. 

1. Dry coal. Long flame. 

2. Fat coal. „ „ 

3. „ ,, Caking coal. 

4. „ „ Short flame. 

5. Lean coal. 



Equivalent Names. 
Non- caking coal. Long flame. 
Gas coal. 
Furnace coal. 
Caking coal. 
Anthracitic coal. 



The following tables give the characters of the different 
coals : 



FUELS— WOOD, PEAT, COAL 



59 



1. Non-caking coal 

Long flame 

2. Gas coal . . 

3. Furnace coal . 

4. Coking coal . 

5. Anthracitic coal 



•{ 





•+i 




a 

4) 


Products of 




H-3 

a 






V o 


Distillation. 


4= 

a 








H^ 










8 

p. 
c 
o 


P. 

a 

9 


S3 

p. 
a 

(30 


P 

O 13 


§p 


a 

<p Pi 


o 
f-l 


o 

§3 
p 


1 

75 


*3 
>> 
W 

5-5 


o 


P4 60 
>> 

o 


S o 


p 


o 
O 


19-5 


4 


12 


18 


20 


50 


to 


to 


to 


to 


to 


to 


to 


to 


80 


4-5 


15 


3 


5 


15 


30 


60 


80 


5-8 


14-2 


3 


5 


15 


20 


60 


to 


to 


to 


to 


to 


to 


to 


to 


85 


5 


10 


2 


3 


12 


17 


68 


85 


50 


11 


2 


3 


13 


16 


68 


to 


to 


to 


to 


to 


to 


to 


to 


89 


5-5 


5-3 


1 


1 


10 


15 


74 


88 


5-5 


60 






10 


15 


74 


to 


to 


to 


1 


1 


to 


to 


to 


91 


4-5 


5-5 






5 


12 


82 


90 


4-5 


5-5 




1 


5 


12 


82 


to 


to 


to 


1 


to 


to 


to 


to 


93 


4 


3 







2 


8 


90 



Nature of Coke. 



(Pulverulent or 
only slightly 
coherent. 
^ Caked, but 
with many 
crevices, soft. 
\ Caked. Mode- 

> rately com- 
) pact. 

} Caked. Very 
compact and 
hard. 
\ Pulverulent or 

> slightly ad- 
J herent. 



1. Non-caking Coal. Long Flame. — These coals con- 
tain a large quantity of oxygen and hydrogen. On destruc- 
tive distillation they yield a large quantity of gas, and leave 
a residue or coke which usually retains the form of the lumps 
of coal heated, and if such a coal be coked in powder the coke 
has little cohesion, and therefore is soft and friable. The 
coals are black or brown in colour, often hard and stony in 
appearance, and give a distinctly brown powder. 

This class includes most of the hard splint coals used for 
blast-furnaces in Scotland and Staffordshire. These coals 
contain a considerable quantity of nitrogen, from 1 to 1-5 
per cent, and on distillation in the blast-furnace yield 
ammonia equivalent to about 25 lb. of ammonium sulphate 
per ton of coal consumed. 

The specific gravity, unless the ash is very high, is about 
1-25, the available hydrogen is very low, and the heating 
power therefore is also low. They burn with a long smoky 
flame, and yield on distillation large quantities of tarry 
matters. 

These coals occur in abundance in the coal-fields of Scot- 
land and also in Derbyshire and Staffordshire. 



60 



FUEL 
Examples of Coaxs of Class 1 





l. 


2. 


3 - 


4. 


5. 


6. 


Volatile matter 


42-3 


42-05 


39-27 


38-90 


42-18 


39-95 


Coke 


57-7 


57-95 


60-73 


6310 


57-82 


60-05 


Fixed carbon . 


54-9 


54-00 


4303 


48-10 


55-27 


56-30 


Ash .... 


2-8 


3-95 


17-70 


15-00 


2-55 


3-75 


Sulphur . 


•88 


115 


•6 


•65 


•53 


1-65 ! 


Moisture . 


71 


81 


10-40 


8-95 







1, Govan, splint. 2, Russell, splint. 3, Overton. 4, Woodhill, wee. 
shire <E. W. T. Jones). 6, Staffordshire, bottom coal (E. W. T. Jones). 



5, S. Stafford- 



2. Gas Coals. — These coals are black in colour, usually 
hard and dense, and have a specific gravity of about 1-3. On 
distillation they yield a large quantity of gas, often as much 
as 20 to 24 per cent, or 11,000 to 13,000 cubic feet per ton ; 
they contain a considerable quantity of nitrogen, and yield a 
good deal of ammonia. The coke left when the powdered coal 
is heated is more coherent than that of Class 1, but is still 
friable and too soft for blast-furnace use. If coked in lumps, 
the lumps fuse together but do not entirely lose their identity. 
On heating, the coals soften somewhat, whence the name 
" fat " coals has been given to them. These coals are in great 
demand for various purposes. They are used for gas-making, 
and are very suitable for use in reverberatory furnaces, as 
they burn with a long luminous flame ; the varieties which 
approach nearly to Class 1 are used in the blast-furnace, 
and many of the Scotch splint coals belong to this class. 

3. Furnace Coals. — These coals are among the most valu- 
able for general use. Many varieties are used for domestic 
purposes, and are commonly called house coals. They are 
suitable for reverberatory -furnace use, and are used for gas- 
making, but are too strongly caking for use in the blast- 
furnace. They are black, have a bright lustre, are often soft 
and brittle (cherry coal). They burn with a bright luminous 
flame. On heating, they soften and swell up, the separate 
pieces adhering and forming a dense gray coke, in which almost 
if not quite all trace of original pieces is lost. The amount 
of coke left on distillation may amount to 75 per cent. 



FUELS— WOOD, PEAT, COAL 

Examples of Coals of Classes 2 and 3 



61 





1. 


2. 


3. 


4. 


5. 


6. 


Volatile matter 


30-60 


31-60 


33-30 


26-40 


25-18 


28-60 


Coke 


69-40 


68-40 


66-70 


73-60 


74-82 


71-40 


Fixed carbon . 


63-20 


64-27 


65-29 


69-06 


67-47 


69-98 


Ash . 


6-20 


413 


1-41 


4-54 


7-35 


1-42 


Sulphur . 




•91 


•749 




•803 




Moisture . 


5-85 


8-85 


6-44 


2-10 







1, Auchenairn, splint. 2, Ell No. 1. 3, Dungarvie, Blackband. 
5, Berlin, Penn. (J. I. and S. I.). 6, N. Wales (Mushet). 



4, Rawkiston No. 2. 



4. Coking Coals, — These coals are black and shining, and 
are usually harder than those of Class 3, which, however, they 
resemble. On heating, they soften, swell up, and apparently 
fuse into a solid coherent coke, which is harder and more 
compact than that left by coals of Class 3, and may amount 
to as much as 80 per cent of the weight of the coal. They 
burn with a shorter flame than those of the preceding groups, 
and give less gas. They are used for household and furnace 
purposes, and for making coke. 

5. Anthracitic Coals. — These coals are bright black, 
and soil the fingers very slightly if at all. They are hard and 
compact, have a specific gravity of 1-35 to 1-4, ignite with 
difficulty, and burn with very little flame or smoke. On 
distillation they yield about 90 per cent of a powdery or 
slightly coherent coke, and give off very little gas. These 
coals are largely used for heating boilers, and are called Blind- 
coals or Smokeless Steam-coals. 

Examples of Coals of Classes 4 and 5 





1. 


2. 


3. 


4. 


5. 


6. 


Volatile matter 


25-90 


2112 


2015 


23-70 


14-2 


10-43 


Coke 


7410 


78-88 


79-85 


76-30 


85-8 


89-57 


Fixed carbon . 


72-71 


77-38 


72-99 


73-56 


81-5 


83-34 


Ash . 


1-39 


1-50 


6-86 


•74 


4-3 


6-23 


Sulphur . 






•88 




1-6 


103 


Moisture . 












1-29 



1, Garesfield (Richardson). 2, Blaina, S. W. (Mushet). 3, Pittsburg, steam (J. 0. 
Weeks). 4, Brymbo, S. W. (Mushet). 5, South Wales, steam coal. 6, Pennsylvania, 
anthracitic coal, 



62 FUEL 

Anthracite. — This coal represents a stage of mineraliza- 
tion beyond ordinary coal. It contains up to 98 per cent of 
carbon. On heating in a closed vessel it gives off very little 
gas, and leaves a residue of 96 to 98 per cent of its weight, 
which is apparently quite unaltered, and shows no sign of 
caking. Anthracite is very hard and brittle ; it is bright, 
usually with a metallic lustre, and often shows iridescent 
colours (Peacock coal). It is extremely difficult to ignite, 
burns without flame or smoke, and gives a very intense local 
temperature. It is used for furnace purposes, and some- 
times for iron-smelting blast-furnaces. 

Anthracite is usually regarded as being coal which has 
been metamorphosed by the action of heat or other agencies. 
This is no doubt the case in many instances, but there is 
evidence that under some conditions ordinary coal may pass 
into anthracite where no heat has been applied, and some 
coals tend to become anthracitic on exposure to the air. 

The same coal-field may yield both anthracites and 
bituminous coals, as in the case of that of South Wales, where 
bituminous coals occur at the east end of the field and 
gradually pass into anthracites at the west end. 

Cannel Coals. — These coals differ so much from the 
ordinary coals that they cannot be placed in the same group 
with them, but must be considered apart. Not only do they 
differ from ordinary bituminous coals in properties and com- 
position, but their mode of formation was probably also 
different. They are close and compact in texture, dull black 
in colour, break along joints, or with a conchoidal fracture, 
and often appear like black shales. They burn with a very 
long luminous or smoky flame, whence the name cannel 
(candle) coal. When heated they decrepitate with a crack- 
ing sound, and therefore are sometimes called parrot coals. 
On distillation they yield a very large quantity — 10,000 to 
16,000 cubic feet per ton — of highly illuminating gas, leaving 
a residue which sometimes consists mostly of ash, and contains 
but little fixed carbon. Cannel coals were formerly used 
entirely for gas-making. At the present day there is no 



FUELS— WOOD, PEAT, COAL 



63 



demand for rich gas. They give a very high yield of tar oils 
when distilled at a comparatively low temperature, and 
fairly successful attempts at recovering these oils for fuel 
purposes were made during the war. 



Examples of Anthracites and Cannels 






1. 


2. 


3. 


4. 


5. 


6. 


Volatile matter 


3-96 


407 


413 


71-06 


66-30 


50-8 


Coke 


9604 


9503 


95-87 


28-94 


33-70 


49-2 


Fixed carbon . 


89-74 


94-10 


89-72 


710 


28-90 


47-76 


Ash . 


6-30 


•93 


615 


21-84 


4-80 


1-44 


Sulphur . 


•585 




•58 


•24 


1-32 


1-76 


Moisture . 


3-71 




3-71 


•4 




315 



1, Pennsylvania. 2, Cwm-Neath, S. W. (Mushet). 3, New Zealand. 
Cannel. 5, Kentucky Boghead (G. Macfarlane). 6, Longton Cannel. 



4, Boghead 



The difference between ordinary bituminous coals and 
cannels is no doubt due to difference in the mode of forma- 
tion, and the latter pass by insensible stages into mere 
bituminous shales. 

Passage from Wood to Coal. — The transformation of 
woody material into coal, and ultimately into anthracite, has 
taken place by a series of very complex changes, the exact 
nature of which is unknown. As decomposition goes on, in 
presence of a very limited supply of air, all the constituents 
of the wood are removed in the form of gases, but at very 
different rates, the oxygen being removed the fastest, next 
the hydrogen, and the carbon most slowly, so that the 
ultimate result is to increase the percentage of carbon in the 
residue as decomposition goes on. The relative rates of 
removal of oxygen and hydrogen are such that though the 
percentage of hydrogen falls, that of the available hydrogen 
increases up to a certain point, when it also begins to decrease. 
Much of the gas which is evolved cannot escape, and is there- 
fore imprisoned in the coal, to be released when the coal is 
cut into in mining operations. The nature of the gases in 
coal-mines therefore gives some indication of the forms in 
which the lost constituents have escaped from the coal. 



64 



FUEL 



The following may be taken as examples of the gases 
found in coal-mines : 

1. 2. 3. 4. 

Marsh-gas (CH 4 ) . .77-5 91-7 66-3 4 

6-32 



Nitrogen (N) 
Oxygen (O) 
Carbon dioxide (C0 2 ) . 
Air . 



211 
1-30 



6-7 
•9 

•7 



4-03 
23-35 



11 



82-00 



It is quite impossible to form any idea of the actual 
amount of material lost, or the relationship which it bears 
to that which is left, but probably the amount lost is enor- 
mously greater than that which remains. 

The following table, from Percy's Metallurgy, illustrates 
the nature of the changes by which woody matter has been 
transformed into coal. Ash, sulphur, and minor con- 
stituents are omitted, and the figures are calculated to 100 
parts of carbon. 



1. Wood 

2. Peat 

3. Lignite 

4. South Staffordshire 10-yard coal 

5. Steam coal, Tyne 

6. Pentrefelin coal, S. Wales 

7. Anthracite, U.S 



Carbon. 



100 
100 
100 
100 
100 
100 
100 



Hydrogen. Oxygen 



1218 
9-85 
8-37 
612 
5-91 
4-75 
2-84 



83-07 
55-67 
42-42 
21-23 
1832 
5-28 
1-74 



Available 
Hydrogen 



1-8 

2-89 

307 

3-67 

3-62 

409 

2-63 



Water in Coal. — All coal as raised from the pit contains 
water in considerable quantity. On exposure to the air it 
loses most of this, till in the ordinary air-dried condition it 
usually retains from 2 to 4 per cent. On heating to 100° this 
water is expelled, but oxidation begins almost immediately 
and the sample increases in weight ; it is therefore im- 
possible to be quite sure of the exact amount of water in coal. 
Perhaps the best way to estimate moisture is to dry the 
powdered sample in vacuo over sulphuric acid at the ordinary 
temperature. Many coals are very hygroscopic, and their 
moisture content will depend on the humidity of the air. 

Sulphur in Coal. — Sulphur is always present in coal 4 ; 



FUELS— WOOD, PEAT, COAL 65 

the amount usually varying from -5 to 3 per cent. The 
sulphur is present in at least three forms. 

The largest quantity is usually in the form of iron pyrites, 
FeS 2 . This is almost invariably present in coal, either in 
thin layers along the planes of bedding or in irregular dis- 
tributed masses scattered through the coal, constituting 
what are called " coal-brasses." Sometimes it is so abundant 
that it can be picked out and used as a source of sulphur for 
the manufacture of sulphuric acid. When coal containing 
pyrites is burned oxide of iron is formed, which remains in 
the ash, 2FeS 2 + 110 =Fe 2 3 +4S0 2 . When such coal is 
heated without access of air, the pyrites is split up, FeS 2 = 
FeS + S, the iron sulphide remains in the coke, and the 
liberated sulphur combining with the carbon forms carbon 
disulphide, which escapes with the gas. Other reactions, 
however, also take place, so that it is not possible to 
calculate from the amount of pyrites the quantity of 
sulphur which will escape as gas and that which will remain 
with the coke. It is the sulphur present in the form 
of pyrites which is most objectionable for iron smelting and 
other purposes. 

Some sulphur is often present as calcium sulphate, 
CaS0 4 . If it remained in this condition it would probably 
not be objectionable for most purposes, but, heated to a 
high temperature with excess of carbon, it is decomposed 
and calcium sulphide is left, which is very deleterious in a 
coal to be used for iron smelting, CaS0 4 +4C =CaS +4C0. 

A third portion of the sulphur is present in some unknown 
state of combination with organic matter. 

Chlorine in Coal. — Chlorine is almost always present 
in coal, though it is usually overlooked, as, unless special 
care be taken in burning, it cannot be detected in the ash. 
The chlorine is probably present in the form of sodium 
chloride, which when the coal is burned is decomposed by 
the silica of the ash, evolving chlorine or hydrochloric acid, 
usually the latter. The following quantities have been 
found by the author in samples of coal : -069, -099, -217, 

(D107> p 



66 FUEL 

•094, -118, -113, -207, -084. These quantities may seem 
small, but they are quite enough to rapidly corrode the 
interior of brass or copper boiler tubes. This is shown by 
the fact that the deposit from the interior of such tubes 
usually contains a considerable quantity of copper-chloride 
or oxy chloride. The presence of chlorine is of little import- 
ance to the metallurgist, but it is of vital importance to the 
engineer who uses the coal for firing boilers fitted with brass 
or copper tubes. 

Phosphorus in Coal. — Phosphorus is always present in 
coal, usually as calcium phosphate ; the quantity, calcu- 
lated on a basis of phosphoric anhydride, P 2 5 , ranging in 
ordinary cases from -1 to 1-25 per cent of the ash. 

Nitrogen in Coal. — All coals contain nitrogen in small 
proportion, though in many analyses this is not stated, the 
nitrogen being taken with the oxygen. The amount is 
largest in the long-flame coals such as the splints, and least 
in the anthracites. When the coals are distilled, about 
15 per cent or more of the nitrogen is evolved as ammonia ; 
50 per cent remains in the coke ; about 5 per cent is con- 
tained in the tar and as hydrocyanic acid ; and the rest 
(about 30 per cent) is evolved as gas. Splint coals contain 
on an average about 1-5 per cent of nitrogen, and anthracite 
coals about «7 per cent. 

Ash of Coal. — All coals leave when burnt a quantity of 
non-combustible residue or ash, varying in amount from 1 
to 10 per cent or more. The ash is quite different in com- 
position from that of wood, and can only to a very small 
extent be regarded as being derived from the original plants 
from which the coal was formed, but mostly as foreign 
matter which has been carried in. Most coal ashes contain 
appreciable percentages of alkali which materially affect the 
fusibility. 1 

The following may be taken as examples of the composi- 
tion of coal ash : 

1 Dr. J. T. Dunn, Journ, Soc, Chem, Ind., 1918, 37, p. 171. 



FUELS- WOOD, PEAT, COAL 



67 



Amount of Ash .... 


1. 
55-2. 


2. 
6-94. 


3. 
2-91. 


4. 
14-72. 


Silica 

Alumina \ 

Oxide of iron . . . . / 

Lime 

Magnesia 

Sulphuric acid (S0 3 ) . 
Phosphoric acid (P 2 5 ) 


40-00 

44-78 

1200 

trace 

2-22 

•75 


28-87 

5695 

5-10 

119 

7-23 

•74 


34-21 

52-00 

6-19 

•66 

4-12 

6-63 


5300 

3501 

3-96 
2-26 

4-89 
•88 


99-75 


100-08 


97-82 


10000 



It will be noticed that the alkalies, which were very 
abundant in the ash of the plants, have disappeared, and 
that the bulk of the ash seems to be made up of clayey- 
matter. It is, however, noteworthy that the plants which 
approach most nearly to those of the coal-measures are the 
only ones the ash of which contains any considerable quantity 
of alumina. 

This residue or ash does not represent the forms in which 
the mineral constituents were present in the coal, as com- 
bustion breaks up all organic or volatile compounds con- 
taining metals, and leaves the metals as oxides. Any iron 
pyrites is converted into ferric oxide, and this imparts a 
reddish colour to the ash, and, other things being equal, the 
greater the content of pyrites the redder will be the ash. 
In the case of coals containing a very high ash, the large 
amount of white residue may completely hide the red colour 
of the oxide of iron. 

The amount of ash is of great importance, and for many 
purposes so is its quality, as, for instance, whether it fuses 
into a clinker or whether it is infusible. The fusion point 
may be as low as 1000° C. or as high as 1500° C. 



[Table 



68 



FUEL 



Amount and Composition per Cent by Volume of the Gas evolved 
from certain coals of northumberland and durham (? at 20° c.) 





Number of Cubic 


Composition of the Gas. 




Centimetres of Gas 
yielded by 100 


















Grammes of Coal. 


CO,. 


O. 


N. 


CH<. 


1. Low Main Seam — 












Bewicke Main Colliery 


25-2 


5-55 


2-28 


85-65 


6-52 


2. Maudlin Seam — 












Bewicke Main Colliery 


30-7 


8-54 


2-95 


61-97 


26-54 


3. Main Coal Seam — 












Urpeth Colliery . 


27-0 


20-86 


4-83 


74-31 




4. Five-quarters Seam — 












Urpeth Colliery (30 












fathoms from surface) 


24-4 


16-51 


5-65 


77-84 


trace 


5. Five-quarters Seam — 












Wingate Grange Colliery 












(74 fathoms) 


91-2 


•34 


trace 


13-86 


85-80 


6. Low Main Seam — 












Wingate Grange Colliery (108 












fathoms) .... 


23-8 


1-15 


•19 


14-62 


84-05 


7. Harvey Seam — 












Wingate Grange Colliery (148 












fathoms) .... 


211-2 


•23 


•55 


9-61 


89-61 


8. Upper or Harvey Seam — 












Woodhouse Close Colliery 












(25 fathoms) 


840 


5-31 


•63 


4405 


5001 



Rarer Elements in Coals. — Arsenic has been found in 
coal in small quantities. This is associated with the pyrites 
present. Its presence is objectionable where food-stuffs are 
exposed to contamination by the absorption of arsenious 
oxide fumes — for example, when coke is used in the heating 
of barley for malting. Many other metals are also to be 
found in very small quantities, such as copper, lead, zinc, 
antimony, vanadium, and even silver and gold. 

Gas in Coal. — Coal, when freshly won, usually contains 
occluded in it a certain quantity of gas. On exposure to the 
air, especially if warm, the gases are slowly given off, and on 
heating to 50° C. they are rapidly expelled. The quantity of 
gas may be many times the volume of the coal, and may vary 
very much both in quantity and composition, as is shown by 
the above analyses taken from Percy's Metallurgy, p. 77. 

It will be seen that the gases are much the same as are 
usually found in coal-mines, which indeed is exactly what 
would be expected. It will also be noticed that the gases are 
of two classes, the one containing little or no marsh-gas, and 
therefore non-explosive, and the other containing a con- 



FUELS— WOOD, PEAT, COAL 69 

siderable quantity of this, and therefore explosive ; and the 
nature of these gases is sufficient to explain why some pits 
are fiery and others are not. The evolution of these com- 
bustible gases in a closed space may account for many 
explosions on shipboard or in other places where coals are 
stored. 

Weathering of Coal. — When coal is exposed to the air 
it undergoes changes which are called weathering. They 
are mostly due to oxidation by the action of atmospheric 
oxygen, and often have a serious effect on the value of the 
coal, reducing its calorific power and diminishing its power 
of coking. Both the carbon and the hydrogen undergo 
oxidation, and the available hydrogen is reduced. Iron 
pyrites present is also partially oxidized, especially in presence 
of moisture, the expansion thus produced often causing the 
coal to fall to pieces. 

These changes take place more readily the warmer the 
coal, and as they all evolve heat, once they start, they are 
likely to go at an accelerating rate, unless the temperature 
can be reduced. Under certain conditions, as, for instance, 
when the coal is stored in close, un ventilated chambers, 
especially if there is much " slack " present, the temperature 
may rise to ignition point, and the mass then take fire. This 
is usually spoken of as the spontaneous ignition of coal. 

Chemical Composition of Coal. — The ultimate com- 
position of coal is easily determined by the ordinary methods 
of organic analysis, but this throws no light whatever on its 
constitution. If the coal be heated in a closed vessel, part of 
the carbon — the fixed carbon — is left in the residue, the 
remainder — the volatile carbon — goes off in the gases. The 
relative amounts of the two forms of carbon are not fixed 
for a particular specimen of coal, but vary considerably 
with the temperature and somewhat with the rate of heat- 
ing ; and as they are the results of destructive distillation, 
by which complex substances are broken down into simpler 
forms, they do not represent in any way the form in which 
the carbon is present in the coal. 



70 FUEL 

Many attempts have been made to ascertain the proxi- 
mate composition of coal by the action of solvents, but they 
have not been very successful. The most elaborate 
researches in this direction were those of Fremy. He found 
that in the case of lignites the brown varieties were partially 
soluble in alkalies, and almost completely so in nitric acid 
and hypochlorites, whilst the black varieties were not acted 
on by alkalies, but dissolved in nitric acid and hypochlorites. 
The bituminous coals did not dissolve in alkalies or in hypo- 
chlorites, but both bituminous coals and anthracites dis- 
solved completely in a mixture of sulphuric acid and 
nitric acid, producing dark- brown solutions containing 
ulmic compounds, which were completely precipitated by 
water. 1 

Valuation of Coals. — The value of a coal will obviously 
be a function of its calorific power ; but it will not vary 
directly with this, for there are many shales and similar 
substances which have a measurable calorific power, but no 
value as fuels. The value of a fuel therefore falls much more 
rapidly than the calorific power. 

No absolute rules can be given for calculating the actual 
money value of a fuel, but the following points must be 
taken into account ; and it must be remembered that a coal 
may have more value for some one special purpose than it 
would have for any other : 

1. Calorific power or absolute heating effect. 

2. Calorific intensity or pyrometric heating effect. 

3. The amount of ash. A large amount of ash is very 
objectionable ; it reduces the amount of combustible 
material present, and its removal and disposal entails 
trouble and expense. The carriage of the ash has to be paid 
for at the same rate as that of the combustible portion of 
the coal, and the ash or clinker will also have to be carted 
away, and for a given amount of heating power more coal 

1 For modern researches see : Fischer and Gluud, Joum. Oasbeleuch- 
tung, 1915, 58; P. P. Bedson, Joum. Soc. Chem. Ind., 1902, p. 241, and 
1908, p. 147; Burgess and Wheeler, Joum. Chem. Soc, 1911, 99, etc. 



FUELS— WOOD, PEAT, COAL 71 

will have to be supplied to the furnace, and this entails more 
labour. The ash usually falls from the furnace hot, and 
carries with it a certain amount of heat. The specific heat 
of ash being taken as -2, and it being heated, say, to 1000° P. 
for each pound of ash, the loss of heat will be -2 x 1000 = 
200 units. 

4. The nature of the ash — its degree of fusibility. 

5. The coking power of the coal. 

6. The length of the flame. 

7. The amount of sulphur, chlorine, etc., which it con- 
tains. These last do not so much alter the value as render 
it unfit for special purposes. 

Pyrites as Fuel. — In some metallurgical operations 
where pyrites is present no additional fuel is necessary, the 
heat evolved by the burning sulphur being all that is required. 
In this case the pyrites must be considered as a fuel. The 
calorific power of sulphur is 4000 B.Th.U., or 2220 C. units ; 
but the combustion of pyrites is not a simple combination. 
The equation 2FeS 2 + 110 = Fe 2 3 + 4S0 2 shows it to consist 
of at least three parts : 

1. Decomposition of two molecules of pyrites. 

2. Formation of four molecules of sulphur dioxide. 

3. Formation of one molecule of ferric oxide. 
The heat values of which will be : 

The heat of formation of FeS 2 is not known. Assuming 
it to be the same as FeS, i.e. that the separation of the 
second atom of sulphur neither evolves nor absorbs heat — 
an assumption which cannot be correct, but which will not 
be far out — then, in C. units, 

1. 23800- x2 = 47600- 

2. 70500+ x4 = 282000 + 

3. 196000+ xl = 196000 + 



= Total heat of reactions, 430400 + 

which, divided by 240, the weight of the two molecules of 
pyrites (FeS 2 ), gives 1790 as the calorific power of pyrites, 
and divided by 128 gives 3360 as the calorific power of 
sulphur when present as pyrites. (In B.Th.U. this =6050.) 



72 



FUEL 



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SOLID PREPARED FUELS 73 

CHAPTER IV 

SOLID PREPARED FUELS — CHARCOAL, PEAT-CHARCOAL, COKE 

Charcoal. — When wood is heated in closed retorts a black 
residue of charcoal is left. This amounts to about 25 per cent 
of the weight of the wood. If finely divided wood, as for 
instance saw-dust, be heated, the charcoal will be in powder ; 
but if a piece of wood be used, the charcoal will retain the form 
of the wood so perfectly that it will show distinctly the annual 
rings of growth of the wood. 

Charcoal was once a very important fuel, but is now only 
used in a few minor metallurgical operations. 

Properties of Charcoal. — Charcoal is dull black, soils 
the fingers slightly if of good quality, but very much if of 
poor quality. It should ring when struck, and should show 
the annual rings of growth very distinctly. It should ignite 
quite readily, and once ignited should continue burning till it 
is completely consumed. The temperature at which ignition 
takes place depends on the temperature at which the charcoal 
was prepared, the higher the temperature of charring the 
higher the temperature of ignition. It is worth noting that 
in the case of charcoal prepared at a low temperature, the 
ignition temperature is always higher than that of prepara- 
tion, so that a hot-air pipe or other source of moderate heat, 
though it may char wood, is not likely to ignite the charcoal. 

Temperature of Temperature of 

Preparation. 1 Ignition. 

3000° F. 1650° C. 2500° F. 1370° C. 

2500 1370 1300 700 

2000 1090 1100 590 

1500 820 900 480 

1000 540 800 430 

500 260 650 340 

Charcoal absorbs gases very readily, and as a rule the lower 
the temperature at which it is prepared the greater is its 

1 Thurston, Materials of Engineering, vol. i. p. 1 84. 



74 FUEL 

absorbing power. Ammonia and hydrogen-sulphide are 
among the gases which are absorbed most readily. Charcoal 
saturated with a combustible gas may take fire on coming 
in contact with air or oxygen. The absorptive power of 
charcoal has been made use of during the war to extract 
ethylene from coke-oven gas for the manufacture of 
" mustard gas." 

The density of charcoal varies with the nature of the wood 
from which it was prepared, the dense woods giving a dense 
charcoal, and the light woods a light charcoal. The specific 
gravity of charcoal varies from about '203 to -134, -2 being 
a fair average. The real density of carbon in the form of 
wood charcoal is about 2, so that the lightness of charcoal 
is due entirely to its porosity. Charcoal absorbs water on 
exposure to moist air, and may under ordinary conditions, 
though appearing quite dry, contain about 10 per cent of 
moisture. 

Composition of Charcoal. — Charcoal is not pure carbon, 
as it is often considered to be, but always contains hydrogen, 
oxygen, nitrogen, and ash. The average composition may 
be taken as carbon 95, hydrogen -5, oxygen 1*5, ash 3-0. 
Charcoal should not lose anything but water on heating 
strongly in a closed platinum crucible. 1 If combustible gases 
are given off it is evidence that the wood has not been 
perfectly charred. 

Charcoal as a Fuel. — Charcoal is an excellent fuel for 
many purposes. In small bulk it burns with a glow at low 
temperature, the product being almost entirely carbon 
dioxide, though a small quantity of carbon monoxide is 
usually formed and frequently escapes combustion. At high 

1 According to Desmond, charcoal when heated to redness gave off 
17 to 25 times its own volume of gas, having the composition: 

Carbon dioxide . . . . . .9-14 

Oxygen -26 

Carbon monoxide . . . . .18-08 

Hydrogen . . . . . . .49-11 

Marsh-gas ....... 16-04 

Nitrogen 7-37 



SOLID PREPARED FUELS 75 

temperature large quantities of carbon monoxide are formed, 
which burn with the characteristic pale-blue flame. Owing 
to the porosity of charcoal, air finds its way into the mass, 
and combustion takes place very readily. Its heating power 
is very high (about 13,700 B.Th.TL). Owing to the way in 
which it burns, and the absence of luminosity in the flame, 
it is better suited for blast-furnaces where it heats by contact, 
or open fires where it heats by direct radiation, than for 
reverberatory furnaces where radiation from the flame is the 
source of heat. 

The ash contains only very small quantities of deleterious 
impurities. Hence charcoal has been used for the pre- 
paration of a very pure iron in blast-furnaces, iron so made 
being called charcoal-iron, and being highly valued. It can 
only be used in small blast-furnaces, as it is very friable and 
crushes easily if the superincumbent charge be too heavy ; 
and for the same reason loss in transit is very considerable, 
often reaching 10 per cent of the weight. 

For domestic use charcoal is very objectionable, unless 
burned in a fireplace with a very good draught, on account of 
the formation of carbon monoxide, which, being odourless 
and colourless, is not easily detected. 

Red Charcoal (Rothkohle). — This is merely wood 
which has been charred at a very low temperature ; it has 
a brown colour, retains much oxygen and hydrogen, and 
is intermediate in composition between wood and charcoal. 

Preparation of Charcoal in Circular Piles. — This 
method of charcoal burning has been in use from a very 
remote period. It is the method which was used in Great 
Britain when charcoal was largely used for smelting iron in 
the small blast-furnaces of the south of England, and it is 
still practised in the east of Europe where charcoal is used 
for smelting purposes. 

A plot of dry level ground is selected, as sheltered as 
possible from the wind, having a slight declination from 
the centre. In the centre three upright stakes, about 7 feet 
long, are driven into the ground at distances of about a 



76 



FUEL 



foot apart so as to form in plan an equilateral triangle, 
and these are kept in position by short cross-pieces of wood 
placed at intervals. 

Pieces of wood cut to a uniform length of about 2 ft. 6 ins. 
are stacked round this central triangular chimney in a series 
of concentric rings, till the heap is 5 or 6 feet in diameter. 
The pieces at the centre are nearly vertical, and the slope is 
made to increase slightly towards the circumference. On the 
top of this is stacked another similar series of pieces of about 
the same length, but placed a little more inclined, and on the 
top of this a layer of brushwood or other small wood, so as 
to give the heap a roughly semicircular section. Round the 




ssMs^ 



bTG. 4. — Charcoal Burning in Circular Piles. 



base of the heap is now driven a ring of Y sticks, so placed 
that the fork is about 6 inches above the ground, and resting 
on these forks is placed a series of bars of wood so as to form 
a ring encircling the heap. A cover is now made by putting 
sods, grass side inwards, over the heap, commencing at the 
ring resting on the forked sticks and terminating at the mouth 
of the chimney, and when this is finished the surface is 
plastered over with moistened charcoal dust so as to make 
it as air-tight as possible. 

The space within the three central stakes is now filled with 
easily combustible wood, which is lighted, and as this burns 
away more is added, till the centre of the pile is well alight. 
Then the top of the chimney is closed with turf, the surface 
of the pile examined, and if it shows signs of sinking any- 
where the cover is quickly removed at the spot, brushwood 



SOLID PREPARED FUELS 



77 



introduced, and the cover replaced, and the heap is left to 
itself for several days. 

The heat of the combustion in the centre of the pile dries 
the wood. The moisture partly escapes as steam, and partly 
condensing on the inside of the cover, runs down and escapes 
as water. This is therefore called the sweating-stage. When 
this is complete the openings round the bottom are closed 
with turf. The cover is again carefully examined, and if it 
shows signs of cracking it is repaired with turf wherever 
necessary, and the heap is left for two or three days. At the 
end of that time a series of openings is made round the foot 
of the pile and another series at about the level of the top of 




FIG. 5. — Rectangular Pile. 

the lower row of wood. Air enters the lower openings, and 
dense yellow smoke escapes from the upper ones. After a 
time the smoke becomes paler and less dense, and ultimately 
is replaced by a pale almost invisible haze. The upper row of 
holes is then closed, and another row is opened lower down, 
where the same phenomena take place, and so on till carbon- 
ization is complete. The openings are then all closed, and the 
heap is left at rest for two or three days, after which the 
cover is removed, the charcoal drawn, and at once quenched 
with sand or water and stacked for the market. The heap is 
usually drawn at night, as then it is much easier to see any 
unextinguished sparks. The whole operation takes about 
ten or fifteen days. These circular piles are called in German 
"Meiler." 



78 FUEL 

The form of heap and arrangement of the wood have been 
modified in different districts. The wood may be stacked 
horizontally instead of vertically, and the chimney may be 
replaced by a solid stake, the heap then being lighted by 
radial passages at the base. 

In Sweden large rectangular piles are used, the wood being 
placed horizontally and transversely, and resting on longi- 
tudinal beams R, so as to allow of the circulation of air under- 
neath. The vertical sides are protected from the air by 
vertical screens of wood, the space between which and the 
ends of the pieces of wood is rammed with charcoal dust, and 
the top and the sloping end is made air-tight with a cover of 
turf or charcoal dust v, exactly as in the circular piles. The 
heap is lighted from a horizontal passage k left near the lower 
end, and when air is admitted it gets in through openings 
below the bottom of the pile. 

Theory of the Process. — This is comparatively simple. 
During the early stages some of the wood in the centre of 
the pile burns, and the heat partially dries the rest. During 
the second stage carbonization goes on very slowly, and the 
whole heap becomes hot. At the expiration of this stage the 
wood in the centre is well charred, that at the circumference 
is only quite dried or slightly charred. When the openings 
are made at the bottom and round the pile a current is set up, 
air enters through the lower openings, travels by the path of 
least resistance, which is along the base of the pile, and then 
up through the partially charred wood, which will have 
shrunk very much, and thus left room for the passage of 
the air. Combustion at once becomes vigorous, the volatile 
matter is distilled from the wood, and dense yellow smoke 
escapes. As the charring is completed the evolution of smoke 
ceases and the charcoal itself burns, and an almost colourless 
vapour alone escapes. The upper holes are then stopped, 
and another row opened lower down. During this third 
stage there will be thus three zones : (1) a zone of charcoal, 
where the carbonization is complete ; (2) a zone of charring 
wood near the opening ; and (3) a zone of dry partially 



SOLID PREPARED FUELS 79 

charred wood. The zone (2) moves downwards as the charring 
goes on. During charring there is a constant shrinking, and 
the cover not being rigid falls down and keeps in contact with 
the surface of the charcoal. 

The gases which are evolved contain nitrogen, carbon 
monoxide, carbon dioxide, and hydrogen. A sample 
analysed by Ebelman gave — 

Carbon monoxide ...... 9-33 

Carbon dioxide . . . . . .25-89 

Hydrogen 9-28 

Nitrogen ....... 55-56 

From the composition of the gases Ebelman concludes that 
the heat of the pile is kept up by the combustion of the fixed 
carbon or charcoal. It seems, however, likely that a con- 
siderable portion at least of the heat may be derived from the 
burning of the combustible gases which are given off. 

Yield of Charcoal. — The yield will naturally vary with 
the nature of the wood and its condition as to dryness, etc., 
and the method of conducting the operation. The yield by 
weight is about 20 per cent, but oftener less than more. 
Percy gives the limits as from 15 to 28 per cent, though it is 
doubtful if the latter figure is ever reached in an ordinary 
meiler. The yield by volume is about 67 to 68 per cent. 

The rate and temperature of charring influence the result 
very much ; the more rapid the charring the less is the yield. 
In one case given by Karsten, an experiment was made with 
young oak-wood, and it gave with rapid charring 15-64 per 
cent, and with slow charring 25-6 per cent. 

Charring in Kilns. — Many forms of kiln have been 
suggested for charcoal burning. They are all similar in 
principle, though they vary very much in detail. One in 
use in America may be described as a type. The kiln is bee- 
hive in form, and is built of fire-brick. It is provided with 
two openings, one (a) at the bottom and the other (b) in the 
dome, which can be closed, when the kiln is in use, by iron 
doors. Near the bottom of the kiln are three rows of holes 
about 3 ins. by 4 ins., and 2 feet apart, the rows being about 



80 



FUEL 



1 foot apart. These holes are stopped with clay when not 
required. The wood used is pine ; it is cut into lengths and 
stacked through the bottom door as far as possible, then the 
charging is continued through the upper door from the plat- 
form (c) till the kiln is full. The charge is lighted through the 
bottom door, the upper door being also left open, and as soon 
as combustion has fairly started both doors are closed and 
luted. The air then enters through the lower openings, and 
the products of combustion escape through the upper ones ; 
and when combustion is complete all the holes are thoroughly 
stopped with clay, and the kiln is allowed to cool. 




Fig. 6. — American Charcoal Kiln. From Eisler's Argentiferous Lead. 

The charring takes about eight days and the cooling about 
four more. Each kiln holds about 3350 cubic feet of wood, 
and produces about 1300 bushels of charcoal. 

The Pierce Process. — This process was devised in 1876 
for the preparation of charcoal and the recovery of by- 
products. It is now largely used in the United States. 
Some of the kilns are made of large size, capable of treating 
as much as 60 tons of wood at one time. 

The wood is heated in brick-kilns, which in the first works 
were 32 feet in diameter and 16 feet high in the centre, and 
held fifty -five cords of wood. The oven being charged with 
wood, gas from a previous operation, together with the 
requisite amount of air for its combustion, is sent in by means 
of steam jets. As the wood dries, steam is given off, which 



SOLID PREPARED FUELS 



81 



is allowed to escape into the air. After about eighteen hours 
the wood is quite dry and distillation begins. The top of the 
kiln is then closed, and the exit tubes are connected with the 
condensers. The products of distillation are drawn away by 
means of fans and passed to the condensing apparatus, and 
the uncondensed gases mixed with the proper proportion of 
air are returned to the kiln. The carbonizing occupies six 
or eight days, after which the kiln is allowed to cool and the 
charcoal is drawn. The whole operation — charging, carbon- 
izing, cooling, and discharging — occupies about eight days. 
There is more gas than is required for charring, and the excess 
is used for raising steam. The kilns are set in batteries of 
sixteen, each set having its own fan and condensers. 

The condensers are a series of copper pipes, set in wooden 
boxes about 4 feet square and 14 feet long, through which 
water circulates. 

The charcoal is said to be excellent quality, and the yield 
is: 

Charcoal 
Methyl alcohol 
Acetic acid . 
Tar . 
Water 
Permanent gases 

The charcoal produced weighs about 20 lb. per bushel, 
that made from the same wood by the ordinary processes 
weighing 16 lb. per bushel. 

Comparison of Methods of Charcoal Burners. 2 



Per Cent. 
25-30 


Per Cord of Wood. 
50-6 bushels. 


•75 


4-4 gallons. 


1-00 


4-6 „ 


400 


16-5 


45-95 


220-7 


23-00 


11,000 c. ft. 



Method of Coking. 


Wood. 


Yield. 


Per Cent 
Vol. 


Per Cent 
Weight. 


Retorts 

Swedish meilers 
American kilns 
American meilers . 


Dry pine 
Fir and pine 
Yellow pine 


81 
52-5 
54-7 
42 


27-7 
18-3 
220 
171 



1 A cord of wood is 128 cubic feet, equal to about 73 cubic feet of solid wood. 

2 Journal of U.S. Association of Charcoal Ironworkers, No. iv., 1883. 

(D107) q 



82 FUEL 

Distillation in Retorts. — In this country most of the 
charcoal used is produced as a by-product in the manu- 
facture of pyroligneous (acetic) acid, by distillation in iron 
retorts. The charcoal obtained in this way is generally of 
inferior quality, because the wood used is selected not for 
its charcoal making quality, but for its yield of pyroligneous 
acid, etc. The yield of charcoal in retorts is much higher 
than that in heaps, often reaching 27 per cent. 

Peat Charcoal. — Peat in its ordinary condition does not 
make a useful charcoal, as the residue which it leaves on 
distillation is very incoherent, and is quite incapable of 
supporting pressure. Many methods have been suggested 
for preparing a good charcoal from peat. They almost all 
consist in pulping the mass, separating the stones and roots, 
pressing into blocks, and then charring in retorts externally 
heated, or in a current of superheated steam. By these 
means a fair charcoal can be obtained, but not one that 
can compete, either in quality or price, with other forms 
of fuel. 

Coke. — When coal is heated without access of air, volatile, 
gaseous, and liquid products are given off, and a residue of 
coke is left, so that coke bears exactly the same relation to 
coal that charcoal does to wood. A coal which yields a 
coherent coke is said to be a coking or caking coal, but 
comparatively few coals yield a good coke. Coke is used in 
a large number of metallurgical operations, for which coal 
is not suited, especially operations carried on in blast- 
furnaces and shallow hearths. 

Coal may be distilled for either of the three products — 
the coke, the gas, or the tar and ammonia liquor, — and in 
each case the others are considered as by-products. In all 
cases special attention is paid to the substance which is 
the chief product and less to the by-products, so that these 
latter are often of inferior quality. Only those processes 
in which coke is the main product will be considered in this 
chapter. 

Properties of Coke. — Coke varies enormously in pro- 



SOLID PREPARED FUELS 83 

perties according to (1) the nature of the coal from which it 
is made, and (2) the way in which the coking is carried 
out. 

In general, three varieties of coke are made : 

(1) Soft coke, often called smithy char, used for smiths' 
forges and similar purposes ; (2) gas coke, used for producers, 
forges, furnaces, and household fires ; and (3) dense or furnace 
coke, suitable for use in the blast-furnace, and in many 
metallurgical operations. 

Soft coke is black and porous. It kindles readily, is soft 
and brittle, and will not stand great pressure. 

Gas coke is variable in quality. As obtained from light 
charges in horizontal retorts and from continuous vertical 
retorts it is generally of rather small size and of open, porous 
texture ; from heavy charges in horizontal retorts and from 
intermittent vertical retorts it is larger and denser. Continuous 
vertical retorts can deliver the coke in a dry state and of a 
good grey colour. In intermittent systems it is advantageous 
to quench the coke with water as rapidly as possible to improve 
the colour and reduce the moisture content. The latter may 
vary between 1 and 25 per cent. 

Furnace coke is hard, dense, and strong, bearing great 
pressure without crushing. It ignites with considerable 
difficulty, and has almost a metallic ring when struck. Coke 
made in the beehive oven has a dark-grey colour, with a 
metallic lustre, and breaks into columnar fragments. That 
made in Simon-Carves and similar ovens was formerly black 
and dull without lustre, and breaks into roughly rhombo- 
hedral lumps. Great improvements in carbonizing and 
particularly in quenching have been made in recent years, 
and there is now little to choose between beehive and coke- 
oven coke. The specific gravity of coke is about -9, and 
as the carbon has a specific gravity of about 2, over 50 per 
cent of the mass must be spaces. Coke is not pure carbon, 
but in addition to the ash it always contains small quantities 
of hydrogen and oxygen, as is shown by the following 
analyses : 



84 



FUEL 





1. 


2. 


3. 


Carbon 

Hydrogen . 

Oxygen 

Nitrogen 

Ash ... 


85-84 

•52 

1-38 

•86 

11-40 


9315 
•72 

•90 
1-28 
395 


84-92 

4-53 

6-66 

•65 

2-28 



1, Dunkinfield (Percy). 2, Best Durham (Kubale). 3, Average Durham (Kubale). 

The best metallurgical cokes contain less than 3 per cent of 
volatile matter and less than 2 per cent of moisture. The 
volatile matter in general may vary from 20 per cent in low 
temperature coke to 2 per cent in high temperature coke. 
In practice, coke is usually assumed to contain 90 per cent 
carbon. 

Strength of Coke. — The crushing strength of coke 
varies. A coke for blast-furnace use should be very strong. 
Good cokes have a crushing strength of from 500 to 1500 lb. 
per square inch. It is, however, much less at high tempera- 
ture ; one sample gave 597 lb. in the cold, but at a red heat 
only 398 lb. 

The density of coke varies very much, as is shown by the 
following : 

Coke. 

Coppee . 

»» • 

Beehive . 



Apparent density. 


Real density 


101 


1-81 


•77 


1-76 


111 


1-78 



Coke as a Fuel. — Coke is an excellent fuel for many 
purposes, but especially for use under such conditions that 
it heats either by contact or by radiation, and where flame 
is not necessary. It has approximately the same calorific 
value as the coal from which it is made when the ash content 
of the coke is not more than about 7 per cent. When the ash 
content is very low the coke may have a higher calorific value 
than the coal, but as a rule there is a drop of about 5 per 
cent owing to the large increase in the percentage of ash. 
It is mainly used in blast and similar furnaces* and in these it 
js ojily the solid carbon whjcli is burnt usefully, any volatile, 



SOLID PREPARED FUELS 85 

combustible matters being expelled before combustion can 
take place, hence the necessity for a well-made coke. 

In the blast-furnace, however, the reactions are complex. 
As the air is blown in, carbon monoxide and perhaps carbon 
dioxide are formed, and as the gas passes upwards any carbon 
dioxide is reduced to carbon monoxide ; and unless there are 
other changes, such as the reduction of metallic oxides, 
practically the whole of the carbon will be carried off in this 
form. The heating value can only therefore be taken as that 
due to the formation of carbon monoxide. 

Two fuels may have the same calorific power and yet 
not be equally efficient in the furnace. Charcoal, for 
instance, weight for weight, gives a higher temperature 
than coke. 

Dr. W. Thourer says that charcoal consists of a large 
number of more or less regularly arranged cells, which are 
joined to one another longitudinally, and the walls of these 
cells are readily porous to gases, and are therefore very 
readily oxidized ; whilst coke consists generally of separate 
unconnected cells, the walls of which are composed of a dense 
vitreous matter which does not admit of the passage of the 
air, and which is very difficult to oxidize ; hence the rela- 
tively lower efficiency in blast-furnace practice of coke as 
compared with charcoal would be increased if it were possible 
to cause the structure and character of coke to more closely 
resemble that of charcoal, either by the formation of a more 
porous, though sufficiently strong coke, or with greater 
certainty, by rendering the coke more easily oxidizable. 

The question of the economical use of fuel in the blast- 
furnace is much more complex, however, than such differences 
would suggest, and will be fully discussed later. 

Coke is admirably suited for domestic use, as its radiative 
power is very high, the chief objections to it being the diffi- 
culty of ignition, the necessity for a deep bed or a good 
draught, and the bulkiness of the ashes. It is usually 
thought that coke contains more sulphur than coal, but this 
is not by any means always the case. 



FUEL 



Sulphur in Coke. — All coals contain sulphur, part of 
which is eliminated during coking and part remains in the 
coke. As a rule the coke contains a smaller percentage of 
sulphur than the coal from which it is made. The sulphur, 
as already mentioned, is present in three forms. That 
present as sulphates remains in the coke probably as calcium 
sulphide ; that present in organic combination passes, at any 
rate to a large extent, into the gases ; and that present in 
pyrites goes partly into the gas and part remains in the coke. 
The total amount of sulphur in the coal does not give any 
definite information as to the amount which will remain in 
the coke, as this depends on the form in which the sulphur 
was present. Even the quantity present in the coal as 
pyrites is not an absolutely safe guide, as changes other than 
the simple decomposition of the pyrites by heat may take 
place ; and Dr. F. Muck asserts that in coke some of the 
sulphur is still present in organic combination, in which form 
it is not acted on by hydrochloric acid, which evolves all the 
sulphur from iron sulphide in the form of sulphuretted 
hydrogen. The only safe method is to determine the sulphur 
in the coal and in the coke derived from it on the small scale. 
As a rule the more iron the ash of a coal contains the more 
sulphur will be retained in the coke. 





Sulphur in Coal. 


Sulphur in Coke. 


1. 


1-47 


1-22 


2. 


1-93 


1-60 


3. 


1-61 


1-32 


4. 


1-26 


•98 


5. 


•84 


•797 


6. 


•74 
1 to 4, Hilgenstock. 


•625 



In ironworks it is often assumed that one half of the total 
sulphur remains in the coke, the other half passing away with 
the gases. Whether the amount of sulphur which passes 
into iron depends on the form in which the sulphur is present 
in the coke is uncertain. 

Nitrogen in Coke. — When coal is coked, a very large 
proportion of the nitrogen, often as much as 75 per cent, 



SOLID PREPARED FUELS 87 

remains in the coke in some form of combination. According 
to W. Foster, when coal is distilled the nitrogen is thus 
distributed : 

In gases as ammonia . . . 11 to 18 per cent. 

„ „ „ cyanogen . . . -2 „ 1-5 „ „ 

Remains in coke . . . . 48 „ 66 „ „ 

Not accounted for . . 21 „ 36 „ ,, 

The amount not accounted for escapes mostly as gaseous 
nitrogen, there being a small percentage which finds its way 
into the tar. 

Coalite. — Some years ago a form of coke was put upon the 
market and much advertised under the name of Coalite. 
This is prepared by coking coal at a low temperature, the 
result being a residue which still contains 10 per cent, or 
more, volatile matter, and is very porous and therefore 
ignites very readily. In the manufacture volatile products 
of considerable value — gas, tar, and ammonia — are given off, 
and can be recovered. The inventor states that 800° F. 
(430° C.) is the best temperature for distillation, and in 
order that the coal may be uniformly heated, retorts of 
special form are used. With coals which do not cake 
strongly, D -shaped metal retorts 7 feet long, 5 feet wide, 
and 16 inches high were recommended, the fuel being spread 
in a thin layer on the bottom, and the coking lasting eight 
hours. In the case of strongly caking coals the coal was 
placed in tapering cylinders 10 or 12 inches long, one end 
being perforated to allow of the escape of the gas given off. 
These were completely filled with the coal, and placed either 
horizontally or vertically in a furnace. After drawing from 
the retorts the coke was quenched with water. In the more 
modern Barnsley installation of low temperature carbonizing 
plant the retorts are vertical ovens, 10 feet long by 10 feet 
high by 12 inches wide. A central movable iron plate 
divides the oven in two. 

There are many difficulties in obtaining by external 
heating satisfactory and economical semi-carbonization of 
caking coals, and furthermore the product is not nearly so 



88 FUEL 

strong as high temperature coke and therefore suffers in 
transport. For these reasons the sale of coalite has not yet 
made great headway. 

The following analysis will indicate the character of 
Coalite : 

On dry basis. 



Fixed carbon . 


1. 

. 80-0 


2. 
851 


Volatile matter 


. 120 


6-4 


Sulphur .... 


10 


1-8 


Ash . 


70 


6-7 


Moisture . . ' . 


(10-3) 


, Average analysis, Prof. V. B. Lewes. 


2, Analysis of 


sample, Author 



Selection of a Coal for Coke-making. — In the selec- 
tion of a coal for coking attention must be paid to various 
properties. The amount of coke which the coal will yield 
is of importance, but less so than its quality. For blast- 
furnace use the coke must be hard and dense, and capable 
of bearing great pressure without crushing, and the higher 
the furnace the stronger must be the coke. Some idea of 
the nature of the coke which a coal will yield can be obtained 
by coking a small quantity in a crucible ; but this is never 
quite satisfactory, as the heating does not take place under 
the same conditions as in a coke-oven, so that an actual 
oven-test is the only safe method of ascertaining the coking 
power of a coal. Coals yielding more than 80 per cent or 
less than 60 per cent of coke in laboratory experiments never 
yield a coke hard or dense enough for furnace use. . The 
coal should be as free as possible from sulphur and ash, and 
for coking should preferably be in a coarse powder. When 
a coal is not sufficiently good in its coking properties it can 
often be made quite suitable by the process of disintegrating, 
wetting (to about 12 per cent moisture) and stamping before 
charging into the horizontal coke-oven. Most coals are very 
much improved by washing, the sulphur and ash being 
greatly reduced. 

Coke-burning in Heaps. — The earliest and simplest 
method of making coke was to char the coal in heaps, 



SOLID PREPARED FUELS 



89 



almost exactly in the same way as charcoal was made from 
wood. The heaps were either round or rectangular, and as 
a rule were larger in diameter but lower than the charcoal 
piles, and a brick chimney was used in place of the three 
wooden stakes above described. The coal was placed with 
the planes of bedding vertical, and as large lumps as possible 
were used. The heap was covered air-tight with breeze 
(coke dust), and the burning conducted much as charcoal 
burning, except that, as coal contains but little water, there 
was no sweating stage. 

This process was in use in a few localities till quite 
recently, even if it is now extinct. Some smelters prefer 
coke made in heaps to that made in ovens, and assert that it 
is freer from sulphur, though this does not seem to be likely. 

Coke-making in Stalls. — In this process the coal 
instead of being coked in an open heap is coked in a space 
surrounded by walls. 
The stalls used in 
Silesia, described by Dr. 
Percy, were about 60 
feet long, 15 feet wide, 
and 6 feet deep, the 
walls being built of 
brick ; a number of 
horizontal passages were left in the wall 
communicated with a vertical chimney. 




Fig. 7.— Silesian Coke Stall. 



each of which 
Wooden poles 

were put through the cross openings, so that when they 
were withdrawn they would leave channels through the coal, 
and the coal was filled in, each layer being stamped down. 
The poles were then withdrawn and fires of brushwood 
lighted in the passages, one end of the passage and the 
chimney on the opposite side being closed. As soon as 
combustion was well started the gases from the distilling 
coal passed downwards and burned on meeting the air, the 
heat thus produced continuing the distillation. As soon as 
gas evolution ceased the process had to be stopped to 
prevent the coke from burning. 



90 FUEL 

Coking in Ovens. — Coke is now usually made in ovens. 

Classification of Coke Ovens. — The following classi- 
fication includes all ordinary types of coke ovens, and the 
chief examples mentioned are described in the text : 

1. By-products are not recovered. 

a. Combustion takes place in the coking chamber. 

Beehive oven, Cox's oven. 
6. Combustion takes place outside the coking 
chamber. (Retort ovens.) 

Appolt oven, Coppee oven. 

2. By-products are recovered. 

a. Beehive type. 

a. Combustion takes place in the coking 

chamber. 
Jameson oven. 

b. Heated from below. 

Pernolet oven. 
£. Retort type. Heated externally. 

a. Without regenerators. Waste heat ovens. 
Bauer oven. Simon-Carves, Otto, Semet- 
Solvay, Simplex, Coppee, Still, C.G.O. 

6. With regenerators. 

Simon-Carves oven, Otto-Hoffman oven, 
Semet-Solvay oven, Otto Hilgenstock oven, 
Koppers oven, Huessener oven, Coppee, 
Simplex, Still, and C.G.O. ovens. 

Beehive Oven. — The oven until recently in most common 
use but gradually getting displaced is the beehive — so called 
from its shape. The form of oven and method of conduct- 
ing the process differ somewhat in different districts ; the 
following description, which is that of the process as carried 
on in a large Scotch works, will serve as a type : 

The oven is built of fire-brick set in clay ; it is 11 feet 
6 inches in diameter at the bottom, and is cylindrical for 
a height of 2 feet 6 inches, and is then domed over, the 



SOLID PREPAEED FUELS 



91 



dome being a little flat, so that the greatest height is 8 feet 
6 inches. Each oven is provided with a working door in the 
front, an opening in the centre of the roof which can be closed 
with a damper, and an opening near the top for the escape of 
the products of combustion, which is so arranged that it can 
be put in connection either directly with the air or with a 
chimney. The ovens are usually built in blocks of twelve or 
twenty -four, so as to prevent, as far as possible, loss of heat 
by radiation. The working opening can be closed by a door 
made up of an iron frame, divided into two parts by a 
horizontal bar about six inches from the bottom. The 




Fig. 8.— Beehive Coke Oven. 

upper space above this bar is filled up with slabs of brick 
luted with clay, a small hole being left near the top by 
which the interior of the oven can be seen, and which can 
be closed with a plug of clay when not in use. The narrow 
space below the cross-bar is filled up as required with fire- 
clay. The door is usually lifted into position and held firm 
by a cross-bar resting in catches in the door frame, but in 
some ovens it is attached to a chain running over a pulley, 
by which it can be readily lifted. 

The charge having been drawn, and the oven being at a 
very dull, hardly visible, red-heat, the damper is closed and 
the charge of about seven tons of coal in the form of slack is 



92 FUEL 

thrown in. While this is being done, an inner or false door 
of fire-brick set in clay is gradually built up so as to keep the 
coal from running out ; this wall is four inches back from the 
main door, and is carried up to the top of the charge. As 
soon as the charge is in, the door is put up and luted, the slit 
along the bottom being also luted, and the damper is opened. 
Combustion very soon begins, if the oven be sufficiently 
hot ; if it be not, a coal fire is lighted on the top of the charge. 
Smoke soon begins to escape, and for about four hours dense 
white smoke is emitted from the top of the oven ; then igni- 
tion takes place, the gas bursts into flame or the coal " strikes," 
and an opening is made at the bottom of the door so as to 
admit a good deal of air. For the next twelve hours the gases 
in the oven burn with a dull smoky flame above the surface of 
the charge. On the second day the flame gets redder, and the 
air supply is diminished by partially closing the opening at 
the bottom of the door with clay. On the third day the flame 
becomes very bright and the air supply is still further reduced. 
On the fourth day the flame becomes very red, and still less 
air is admitted, and by the end of this day no more flame is 
seen coming off from the coke, and the whole interior of the 
oven is red-hot, the bricks inside being distinctly visible 
through the sight-hole. All the gas now being off, the space 
below the door is thoroughly luted with clay, but the damper 
is left open for about six hours longer, when it too is closed 
and luted. The oven is thus closed air-tight and is left in 
this condition for about twenty-four hours, by which time the 
coke will have considerably cooled, and by the end of the 
fifth day (120 hours) from charging the oven will be ready for 
discharging. The outer and inner doors are taken down, and 
a few bucketfuls of water are thrown into the oven. This 
water is at once converted into steam and thus cools the coke 
so that it can be drawn. When the coke is cool enough a bar 
or " shackles " is hung across the top of the door, being 
suspended on pins in the masonry ; on this hangs a pulley 
on two flanges. A long iron " cleek " or hoe with a heavy 
head is put through between the flanges, the handle resting 



SOLID PREPARED FUELS 



93 



on the pulley, and by its means the coke is drawn out into an 
iron barrow, in which it is wheeled away to the yard and is 
ready for riddling for sale. When the exposed surface of the 
coke is seen to be red-hot more water is thrown in, and so on 
till all the coke is drawn and the oven is ready for recharging. 
Each charge of 7 tons of coal yields about 4 or 5 tons of 
coke, or about 60 per cent ; the same coal yielding in the 
laboratory about 70 per cent of coke. Very frequently the 
coal is charged in through the charging-hole in the roof, and 




Fig. 9. — Discharging Coke Ovens. 

the coke is cooled by throwing in water from a hose for 40 
minutes. 

Theory of the Process. — This is very simple. The heat 
of the oven causes distillation to begin, and the resulting gas 
coming in contact with air burns and thus more heat is 
evolved, the whole heating taking place from above down- 
wards. This is undoubtedly the best method of heating coal 
for coke-making, for the dense hydrocarbons coming up from 
the distilling coal and coming in contact with the incan- 
descent coke are decomposed, permanent gases are evolved, 



94 FUEL 

and carbon is separated. This has some effect on the yield, 
but still more on the quality of the coke, giving to beehive 
coke a peculiar tubular structure. The bubbles of gas as 
they ascend are often decomposed bubble by bubble, leaving 
thin shells of carbon joined together so as to form long hair- 
like tubes. The coke at the top, and also that at the bottom 
of the oven in contact with the floor, is softer and more 
porous than that in the body of the oven, and these portions 
are usually separated and sold for purposes for which dense 
coke is not necessary. As the coke cools it breaks up into 
more or less prismatic masses, and is of a steel-grey colour. 
This is said to be due to the thorough escape of the gas, 
obtained by leaving the damper open some time after all the 
gas seems to have been driven off ; if this be not done, but 
the damper closed at once, or if the coke be drawn immedi- 
ately all gas appears to be off, the coke comes out black and 
lustreless. 

Smithy Char. — This is made in similar ovens and of 
the same coal. The oven being hot, 10 cwt. ot coal is 
thrown in, then at intervals two more charges of the same 
weight are added, and the whole operation is completed in 
twelve hours, 48 cwt. of coal yielding about 38 cwt. of coke, 
or nearly 80 per cent. 

Modifications of the Beehive Oven. — This process, 
modified in various details, but the same in principle, 
is used all over the world, and many coke makers and 
users contend that it gives a better coke than any other 
process. 

The Welsh Oven. — "This consists of a rectangular 
chamber covered with a flat arch, and provided with a door 
at one end. The width of the oven is from 7 to 8 feet, the 
length 13 to 15 feet, and the height does not exceed 5 feet. 
The oven is provided on the top with one or two charging holes 
and in the front with a lifting door. One oven is separated 
from the next by a relatively narrow wall not exceeding 2 feet 
in thickness. The back wall of the oven is also provided with 
an opening through which the waste gases escape to reach the 






SOLID PREPARED FUELS 



95 



flue, leading the same to the chimney, and before doing so are 
in many cases utilized for heating boilers.' ' * 

The oven is charged from the top, and " strikes " from the 
"heat of the oven itself. The heating is partially from above, 
partially from the sides. Owing to the thinness of the side 
walls the structure of the coke, except that from the centre 
of the oven, is not columnar as in the beehive oven, but has 
a conical, or, as it is often called, " cauliflower " structure. 
The average make is 6 tons 5 cwt. per week, and the yield 
58 to 60 per cent. 

Connellsville Ovens. — At Connellsville, Pennsylvania, 
the great coke district of the United States, beehive ovens 




Wi-wM 



'** ■ 'i iV ■*>•* '.'•!•'• '• '•*'. '•' ■ 



'-m%mm 



Fig. 10.— Connellsville Coke Oven. 



have been used exclusively until recently. They are about 
12 feet in diameter and 7 feet high in the clear. They are 
charged through a hole in the roof, and each oven holds 4 J to 
6 tons of coal. The charge is levelled through the working 
opening, which is then walled up with brick. Coking is 
completed in about 72 hours. The door is taken down, 
water is sprayed in with a hose to cool the charge, which is 
then drawn. The yield is about 67 per cent. 

The ovens are built of brick faced with sandstone, and are 
arranged either in single rows on the hill-side (bank ovens) or 
in double rows (block ovens). 

Sources of Loss. — The beehive oven, though it yields an 
1 B. De Soldenoff, J J. and S.I., 1894, ii. p. 215. 



96 FUEL 

excellent coke, is not by any means an economical apparatus, 
as there is considerable loss both of matter and of energy. 
The sources of loss of matter are : 

1. Coke consumed. 

2. The products of distillation, liquid and gaseous, are 

lost. 
The sources of loss of energy are : 

3. Heat lost by radiation, especially during charging 

and discharging, and in the interval between these. 

4. Heat carried away by the products of combustion. 

5. The potential energy of the combustible products of 

distillation and partial combustion. 

The loss under the first head is very considerable, fre- 
quently amounting to 10 or 15 per cent, and it can only be com- 
pletely prevented by the use of an oven in which no air is 
admitted to the coking chamber. Many suggestions have 
been made for minimizing it in the ordinary oven. The inner 
door already described does something, but not much. A far 
more efficient arrangement is to construct a circular air- 
passage in the masonry of the oven above the level of the 
charge, with openings by which the air can enter the oven. 

The loss under the second head is prevented by the use of 
suitable ovens and condensing plant. 

The loss of heat by radiation is reduced by building the 
ovens in blocks of 12 or 24, so that the four end ovens have 
only two sides exposed to the air, and all the rest only one, 
and by covering the roof with a layer of non-conducting 
material such as sand. The loss during charging and dis- 
charging can be much reduced by performing these operations 
expeditiously by means of mechanical appliances. 

The waste heat carried away by the products of com- 
bustion is almost always lost, though it is occasionally used 
for raising steam, and the heat due to the combustion of 
the products of distillation is at any rate partially used in 
promoting coking. 

The Appolt Oven. — This oven, invented by the Brothers 
Appolt, is probably the most important of all the modern 



SOLID PREPARED FUELS 



97 



forms of oven in which the by-products are not recovered, 
and it is designed to prevent all chance of any of the coke 
being burned during the operation, and also to promote rapid 
and uniform coking. These objects are attained by coking 
in a separate chamber heated from outside by the combustion 
of the products of partial combustion. The coking chamber 
is in the form of a vertical fire-brick retort about 4 feet 
long and 1 foot 




W* 



6 inches wide at 
the base, and 3 
feet 8 inches long 
and 13 inches 
wide at the top, 
and about 16 feet 
high. Twelve to 
twenty - four re- 
torts are built 
together into a 
block in such a 
way that an air 
space 8 or 9 
inches wide is 
left round each 
of them, and the 
whole is enclosed 
in very thick 
walls. The retorts are held in position by cross bricks built in 
at intervals, tying them to the outer wall or to each other. 
The top of each retort is narrowed and provided with a charg- 
ing hopper, and the bottom is closed by an iron door or pair of 
doors, opening outwards into a vault extending under the 
whole length of the retorts. In this vault rails are fixed so that 
trucks can be run under to receive the coke. The interior 
of each retort is connected with the outer space by two or 
three series of openings — one set near the bottom, another 
near the top, and sometimes a third about half-way up, and 
air is also admitted from outside, 

( D 107) H 



FIG. 11.— Appolt Coke Oven. A, Coking chambers. 
C, Lower tier of holes.' 



98 FUEL 

The retort having only just been discharged, the bottom 
doors are closed, a charge of about 1J tons of finely -divided 
coal is let in, and the top is closed. The retort being very 
hot, distillation commences at once, and the products pass 
through the openings into the outer space, where they burn ; 
thus each retort is surrounded by a mass of flame, and since 
no air enters it, combustion of the coke is impossible. When 
coking is complete, the bottom doors are opened, and the 
charge falls out into an iron truck placed beneath, and is at 
once quenched with water. 

The retort being heated all round, coking is very rapid 
and uniform and is completed in about 24 hours, and the 
work is so arranged that one retort is discharged and re- 
charged every hour. When an oven is being newly lighted, 
temporary bars are put across the bottom of the retorts, 
and fires are kindled on these till the temperature is high 
enough for distillation, after which the ovens are charged 
in regular order. 

The yield in these ovens is large, about 10 per cent higher 
than that from the same coal in beehive ovens, and the coke 
is hard, dense, and of excellent quality. The first cost of 
the ovens is high. 

The Coppee Oven. — These ovens, which have been also 
largely used on the Continent, are based on exactly the same 
principle as the Appolt oven, but the arrangement of the 
retorts and combustion chambers is quite different. The 
retorts are horizontal chambers about 30 feet long, 18 inches 
wide, and 4 feet high ; they are built of fire-brick in stacks 
of 22, 24, or 50, side by side, and are worked in pairs, one 
being charged when the coal in its neighbour is half -coked 
The oven tapers slightly from back to front, and is closed 
at each end by two well-fitting iron doors, the lower door 
being about 3 feet high, and the upper 1 foot. In the roof 
are a series of hoppers for charging, and each retort com- 
municates by openings near the top with the combustion 
chambers outside. 

The oven being hot, the lower doors at each end are 



SOLID PREPARED FUELS 



99 



closed and the coal is let in through the charging hoppers, 
and is quickly levelled by means of rakes through the upper 
doors, which are then closed. The products of distillation 
pass out of the retorts into the vertical flues between them, 
where they mix with air and burn. The products from the 
two contiguous retorts pass together into the horizontal 
flue under one of them, back under the other and to the 
main flue, and thence to the chimney, being often used on 
the way to raise steam. 

When coking is complete, the doors at both ends are 




Fig. 12. — Ccppee Coke Oven, v, Vertical flues between retorts. H, Horizontal flues, 
c. Flue connecting contiguous horizontal flues. P, Passage to main gas flue. 

opened and the coke is forced out at the wider end of the 
oven by a ram carried on a truck running on rails behind 
the ovens, and is instantly quenched with water. 

The whole operation of charging occupies only about 
eight minutes. The coking occupies from twenty -four to 
forty-eight hours, and the coke yielded is hard and dense. 

The Bauer Oven. — This oven is a modification of the 
Appolt or vertical retort type of oven, arranged so as to 
allow of the recovery of the by-products. Many such ovens 
have been devised, but this one may be taken as a type 
since it has probably been more largely used than any other. 

The stack is circular, the ovens being arranged in a 
series of forty round a central chimney, the retorts being 



100 



FUEL 



therefore placed radially. Each retort is 10 feet high, 6 
deep, and about 1 foot 4 inches wide at the bottom, tapering 
to 1 foot at the top ; the bottom of the retort is curved, so 
that when the iron door is opened the coke can slip out into 
a truck placed in front. The charge is introduced through a 
charging hopper at the top. The products are drawn off by 
a pipe, and after passing through the condensers the gases 
are returned to the oven. They pass into a combustion 




Fig. 13. 



-Bauer Coke Oven at Dairy. From Engineering. Left-hand, section through 
coking chambers : right-hand, through heating flues. 



chamber, where they are mixed with air which has been 
admitted by a passage at the bottom, and heated by con- 
tact with the hot walls of the regenerative chamber. The 
burning gases pass down behind the retort, more air being 
admitted if necessary. The products of combustion circu- 
late through heating chambers between the retorts, through 
the alternate passages of the regenerator and away to the 
chimney. 

If condensation is not required the gases may be passed 
at once from the retort to the combustion chamber. 

Each retort holds two tons of coal, so that the whole 



SOLID PREPARED FUELS 101 

charge is eighty tons, and the time occupied in coking is 
twenty -four hours. 

It is claimed that this oven yields a good strong coke and 
a large quantity of by-products. 

The ovens are not necessarily arranged in circular form, 
but may be in rectangular blocks. A block of this form of 
50 one-ton ovens at Creusot had up to 1886 worked 1800 
charges ; of these 100 were carefully weighed, and the yield 
was 80| per cent of coke. 

The Simon-Carves Oven. — Of the different forms of 
oven arranged for the recovery of the by-products this is one 
of the most popular in this country. It is a modification of 
the Coppee oven, or rather, perhaps it should be said, is of the 
Coppee type, with arrangements for the recovery of the by- 
products. The retorts are horizontal, 30 feet long, 2 feet 
wide, and 6 feet 6 inches high, and they are built in blocks 
of 20 to 60. The roof is covered with a layer of sand or 
non-conducting material and is provided with three open- 
ings, the middle one connected with the condensing plant 
and the other two fitted with charging hoppers for the 
introduction of the charge. The ends are closed with iron 
doors, near the top of which are two openings also closed by 
iron shutters, through which tools can be introduced for 
levelling the charge. The oven being hot from the previous 
charge, the doors are closed, the fresh charge let in and 
levelled as quickly as possible, and the small openings then 
also closed. Distillation at once commences, and the pro- 
ducts of distillation are passed through condensers, where 
the condensible products are separated and the permanent 
gases are returned to be burned under the oven. A small 
fire is kept burning to make sure that the gas shall not be 
extinguished, and the burning gas passes along under the 
whole length of the oven, back again, and then circulates 
through flues between the walls, by which means the retort 
is thoroughly heated. The products of combustion on their 
way to the chimney pass through alternate passages of 
a fire-brick chamber or recuperator, through the other 



102 



FUEL 



passages of which the air necessary for the combustion of 
the gas is passed, so as to become heated on its way. The 
coke is expelled from the oven by means of a ram carried 
on a truck running on rails behind the oven, and is at once 

/ 




Figs. 14 and 15. — Simon-Carves Coke Oven. Section through chamber and 
through flues. 

quenched with water. The coking takes forty-eight hours. 
The coke is hard and compact, but is not so dense or lustrous 
as the beehive coke. As no air finds its way into the oven, 
no coke can burn, and the yield is high, over 10 per cent 



SOLID PREPARED FUELS 



103 



more than in beehive ovens, and the products of distillation 
are very perfectly recovered. 

The Otto- Hoffman Oven. — This oven is of the Coppee 
type, i.e. it consists of horizontal retorts placed side by side. 
The arrangements for charging by openings in the roof, and 
discharging by means of a ram from one end of the retort, 
are almost exactly the same as in the Simon-Carves oven. 
The difference is in the arrangement of the flues, and in the 
use of a regenerator to heat the air before the combustion of 
the gas. Two regenerators are used, which are alternately 
heated and used for heating the gas. They are long chambers, 
filled with a chequer-work of fire-brick, placed underground 




Fig. 16. — Simon-Carves Coke Oven and Recuperator. A, Coking chamber, u. Charging 
trucks. M, Gas main. P, Return gas main. S, Combustion chamber. R, Recuperator. 
d, d', d", Air passages, e, e', Chimney passages. G, Ram. 

and extending the whole length of the set of ovens. At one 
end they communicate with the chimney, and with the 
source of air supply — a fan or blower of any type — com- 
munication with either being opened and closed by means 
of a valve as required. A combustion chamber under each 
oven also communicates with the top of the regenerator by 
means of a valve. This combustion chamber is divided in 
two by a cross wall, so that there is no direct communication 
from one regenerator to the other. Each half of the com- 
bustion chamber communicates with a series of vertical flues 
in the wall of the oven by means of openings, and the flues 
from both combustion chambers enter a horizontal flue about 
the level of the top of the ovens. The coke having been 
withdrawn, the fresh charge is let down, levelled, and the 
doors are closed ; distillation commences, the products pass 



104 



FUEL 



through the condensers, and the gases are returned to one 
end of the combustion chamber under the retort, where they 
meet hot air from the regenerator, and combustion takes 
place. The products of combustion pass up the one set of 
vertical flues into the horizontal flue, down the other set into 
the other half of the combustion chamber, and away through 
the regenerator to the chimney. About every hour or so the 
direction of the air and gas is changed, so that the regenerator, 
which before was being heated by the products of combustion, 




Fig. 17. — Otto-Hoffman Coke Oven. R 1 , R 2 , Regenerators. S, Combustion chamber, 

o, Upper flue. W, Vertical flues connecting o and S'. F o, Charging openings, 

v, Gas mains, c, Lateral openings from vertical flues. d, Hot-air passage from 
regenerator, g, Return gas main. 

now heats the air, whilst the other receives the hot products 
of combustion. 

By use of these regenerators a very high temperature can 
be attained, the temperatures given by Dr. Otto being — 



In the combustion chamber 
In the vertical flues ..... 
In the regenerator, when air was first admitted 
One hour afterwards .... 

In the chimney ..... 



2200°-2550° F. 
2000°-2200° F. 

1800° F. 

1330° F. 
800°- 930° F. 



The charge to the oven is about 5J tons, and coking is 
complete in about 40 hours. 

The Otto-Hilgenstock Oven. — This is a modification 
of the original Otto oven, the improvement being mainly in 



SOLID PREPARED FUELS 



105 



the way in which the gas is burned. The ovens are of the 




usual long retort type, about 33 feet long, 20 inches wide in 
the middle, and 5 feet 11 inches high, each oven usually hold- 



106 FUEL 

ing about 5 tons of coal. The gas is carried away to the con- 

5> 







densing plant, and when freed from condensible substances is 



SOLID PREPARED FUELS 107 

brought back by the pipe d to the distributing pipes e, thence 
by vertical pipes into the larger vertical pipes which open into 
the horizontal flues beneath the vertical flues in the partition 
walls between the ovens. These pipes form large Bunsen 
burners so that air for combustion is drawn in, and combus- 
tion takes place in the vertical flues f. The products of 
combustion pass down by the flues h to the horizontal passage 
under the ovens and thence by the flue m to the chimney, 
or they may be passed under boilers for steam raising. 

The advantages claimed for this oven are uniform heating, 
short heating flues, and full utilization of the heating power 
of the gases, the yield of coke is good, the quality is good, and 
the oven is very durable. As more gas is produced in the 
ovens than is required for heating them, the excess can be 
used for driving gas engines or for any other purpose. 

The Koppers Oven. — In this oven the arrangement of 
the heating is very similar ; the gas is burnt by burners under 
the vertical flues, but the longitudinal connecting flues do not 
go from end to end but are divided in the middle so that the 
oven is heated alternately from each end. The air is heated 
in a regenerative chamber as in the Otto-Hoffman oven. 
The burners are so arranged that they can be lifted out and 
replaced from above, and the partition walls are built of 
" specially moulded fire-bricks, and it is claimed that the 
rhomboidal shape adopted ensures tight joints and prevents 
leakage." The oven was originally designed to work with 
blast-furnace or producer gas, so that the richer coke-oven 
gas might be used for other purposes. 

The Semet-Solvay Oven. — This oven, which has come 
largely into use, is of similar type. The coking chambers 
or retorts are 10 metres long, 1-7 metres high, and from -350 
to -500 metre wide, according to the nature of the coal being 
coked ; the " rich coals with a high percentage of volatile 
matter should be treated in wider ovens, lean coal with a 
small percentage of volatile matter should be treated in 
narrow ovens." x The ovens are built in batteries, as in the 

1 Darby, J.S.C.I., 1895, p. 337. 



108 



FUEL 



case of other recovery ovens. The chambers consist of walls 
of brick covered with arches, well protected to prevent radia- 
tion. These chambers form the skeleton, and are " filled in 
on each side of each supporting wall by channel bricks con- 
taining the heating flues. These channel bricks are rebated 
one into another so as to break the joints, and as they have 
only their own weight to support, there is no fear of cracking 




FiQ. 20. — The Semet-Solvay Coke Oven. 

or bulging when they are highly heated and when the process 
of coking is proceeding." * 

The coal is charged in through hoppers in the roof, and is 
discharged by a ram through the end doors. The gases are 
drawn away through an opening in the roof, passed through 
the condensers, and delivered, together with heated air, into 
the top horizontal flue at the ram end of the oven. They 
pass the whole length of the oven, and descend into the next 

1 Darby, J.S.C.I., 1895, p. 337. 



SOLID PREPARED FUELS 109 

flue, where they meet another supply of gas and heated air ; 
then back along the third flue and into the common flue 
under the oven, where the gases from the two sets of flues 
meet, and the hot gases may be used for steam raising on 
their way to the chimney. The air is heated by passing 
through flues under the hot floor of the oven. 

The time of coking is about 24 hours, and each oven 
holds about 4 tons of coal. 

Among the advantages claimed for this oven are the ready 
heating, owing to the thinner walls of the heating flues (these 
being able to be made thin as they have only their own 
weight to support) and the readiness with which the parts 
can be replaced. 

The Huessener Oven. — This is an oven of a similar 
type. Part of the gas enters a flue under the oven, passes 
along the whole length, is carried up and then into a series 
of horizontal flues in the wall of the oven. In each of these 
horizontal flues more gas and air are supplied, so as to main- 
tain a high temperature, and the products of combustion are 
finally carried away by a flue, their sensible heat being used 
to raise steam. Between each pair of ovens there is a wall 
of fire-brick which carries the roof of the oven, and the heating 
flues are arranged on each side of this, so that each coking 
chamber has an independent series of flues on each side of it. 

Coke from Non-caking Coal. — Coals which have but 
little caking power can sometimes be coked by using a very 
high temperature. It has been suggested to make coke from 
such coals by mixing them with slack of coking coal, pitch, 
tar, or other adhesive materials ; but the cokes thus obtained 
are usually of very inferior quality. 

Coal Compression. — It has long been known that the 
coke obtained from many coals was greatly improved if the 
coal was compressed before coking. Many attempts were 
made to carry out the compression in a rough-and-ready way 
by loading the coal with heavy weights after it had been 
charged into the oven, or by forcing the discharging ram 
against the coal, the discharge door being closed, but such 



110 FUEL 

methods were both inconvenient and unsatisfactory. Within 
the last few years several machines have been devised for 
compressing the coal before it is put into the oven, the best 
known of the older types being that of Kuhn, made by 
Messrs. Kuhn & Co. of Bruch, Westphalia, which may be 
taken as a type. In this type of machine the coal is com- 
pressed into a solid block before it is put into the oven. A 
machine running on rails on the charging side of the oven is 
used, forming a carriage which can be drawn along to any 
oven as required. This carriage carries a strong iron plate 
about the same size as the bottom of the oven, which can be 
pushed into the oven, and which serves as a sort of " peeler " 
on which the block can be pressed and charged into the oven. 
At one end of the set of ovens is a raised platform along 
which the trucks carrying the coal can be run ; in front of 
this is the compressing box, built up of strong iron plates 
so arranged that when fixed in position they form a box the 
interior of which is very slightly smaller than the interior 
of the oven, and the bottom of which is the peel on 
the carriage already mentioned. Above this box is fixed a 
stamper worked by a mechanism so that it can be lifted and 
then pressed down. The coal is run into the stamping box in 
small portions at a time, each layer being compressed before 
the next is put in. When the box is full, the sides are turned 
up, and the block of coal on the peel is moved till it is 
opposite the oven which is ready to receive it and which has 
just been discharged, and the peel with its load is pushed 
into the oven. The door on the charging side is then put in 
place and fixed, a space being left beneath it for the peel. 
As soon as the door is fixed the peel is withdrawn and 
the mass of coal is left in the retort. The time occupied in 
filling, stamping, and charging is about 20 to 25 minutes, so 
that one compressor can serve about 60 ovens if the time of 
coking is over 30 hours. The coal is well moistened so that 
it may cohere, and 10 to 12 per cent of moisture should 
be present. The coke produced when a stamper is used 
is very firm and compact ; the output is not increased 



SOLID PEEPARED FUELS 111 

because, although the compressed coal occupies less space and 
the ovens can hold a larger charge, the charge takes much 
longer to carbonize. The coal is compressed about 25 per 
cent, but the block must be a little smaller than the oven 
so that it may be readily inserted. 

By-products Recovered. — The by-products recovered 
are tar and ammonia and benzol. The tar varies in quality 
according to the temperature of distillation, but is rich in 
members of the benzene series. It is redistilled and various 
products are obtained, such as crude naphtha, benzol, light 
oils, creosote oils, etc., and a residue of pitch is left. The 
total amount of tar is about 4 per cent of the weight of the 
coal used. The amount of sulphate of ammonia obtained is 
about 1 per cent of the weight of coal used, or say 23 lb. 
per ton. Benzol is extracted from the gas, the amount 
recovered averaging about 2 gallons per ton of coal. 

Comparison of Coke Ovens. — It is not easy to compare 
the relative merits of coke ovens, because so many points 
have to be taken into account, and the various types have 
not been tried side by side on the same quality of coal ; and 
even if they were, it would probably be impossible to select 
a best, for what would be best under one set of conditions 
would not be best under another. The beehive oven is 
excessively wasteful ; not only are all the by-products lost, 
amounting, in Great Britain, to no less than 60,000 tons of 
ammonium sulphate per annum, in addition to enormous 
quantities of tar and other products, but there is a loss of 
10 per cent or more of coke actually burned in the process, 
probably equivalent at the present time to nearly half a 
million tons per annum. 

All this might be saved by the use of the recovery 
ovens. 

The Coal Conservation Committee of the Ministry of Re- 
construction in their final report, 1918, give 14-6 million tons 
as the amount of coal carbonized in by-product ovens for the 
year 1916, as against 5-5 million tons from all other types, 
making a total of 20*1 million tons of coal converted into 



112 



FUEL 



metallurgical coke. They point to the rapid decline in the 
number of beehive ovens in recent years : 



Year. Number of Beehive Ovens. 


1910 


16,037 


1911 


14,301 


1912 


13,833 


1913 


13,167 


1914 


9,210 


1915 


7,521 


1916 


6,892 



They supply the information that in November 1917 
some 8700 by-product ovens were in operation in Great 
Britain, of which 8000 were fitted with benzol recovery 
apparatus ; the following table showing the numbers and 
total capacities of the different types of ovens in use : 







Number of Ovens 




Total Rated 


Make of Oven. 








Carbonizing 
Capacity. 










Built and in 


Regenerative 


With Benzol 


Million tons of 




operation. 


type. 


Plants. 


coal per annum. 


Otto 


2290 


553 


2234 


4-91 


Simon Carves 


1876 


870 


1876 


2-75 


Koppers 


1588 


1588 


1522 


3-50 


Semet-Solvay 


1417 


96 


1417 


2-88 


Simplex 


463 


93 


416 


100 


Coppee . 


369 


60 


369 


0-74 


B.C.O. . 


65 


25 


65 


0-18 


All others 


(632) 




(101) 


1-50 


Total . 


8700 




8000 


17-46 



Coke experts are agreed there is little to choose between 
beehive coke and the best by-product oven coke. 

Fig. 21 illustrates a modern successful type of coke 
quencher — the Goodall machine. This consists essentially of 
a massive rotating table receiving the coke from a Darby 
quencher. The coke is carefully extinguished so as to 
minimize the final water content, and a movable plough 
allows it to pass over a screen direct into the wagon. 

Removal of Sulphur from Coke. — Sulphur is very 
objectionable in coke, and many attempts have been made 
to prepare a coke containing but little sulphur, but up to 



SOLID PREPARED FUELS 



113 



the present without success, except by purifying the coal by 
washing before coking. 




When hot coke is quenched with water, hydrogen sulphide 

(D107) j 



114 FUEL 

is sometimes evolved in small quantities by the action of 
the water on the sulphides : FeS +H 2 =FeO + H 2 S, CaS + 
H 2 =CaO + H 2 S, and it has been suggested to make use of 
this reaction for the desulphurization of coke, by treating 
it with superheated steam. In some experiments Scheerer 
found that by treating a coke containing -71 of sulphur about 
60 per cent of this was removed, the residue only containing 
•2 per cent ; but such results have never been obtained on 
the large scale. It is impossible to make the steam reach 
every particle of the coke, and if the temperature is at all 
high the coke itself is acted on by water with evolution of 
hydrogen and carbon monoxide. Treatment with dilute 
acid has also been suggested, but the removal of the sulphur 
is very partial. 

Mr. Calvert suggested mixing the coal before coking with 
common salt, a complex series of reactions being said to 
take place by which sulphur would be evolved. Many other 
methods have been suggested, but none have been successful. 

Comparison of Coal and Coke. — Weight for weight, 
coke has, on an ash -free basis, practically the same 
calorific value as coal, but compared with the coal from 
which it is obtained the heating power of coke is much 
less, so that the loss of heating power by coking is very 
considerable. Even if the by-products are recovered, a 
considerable amount of heat will be used in distilling the 
coal. The whole of this heat, however, would not be 
recovered if the coal were burned in an ordinary fire- 
place, for the gas is there distilled out and then burned. 
When the flame is required, as in a reverberatory furnace, 
coal is best ; but when the heating is to be by contact or 
by radiation, coke is preferable. In cases where the produc- 
tion of smoke is very objectionable, coke is used, though, for 
boilers and similar furnaces, it is not so suitable as coal ; 
used by itself, it requires forced blast, but, when sandwiched 
between layers of coal, it burns freely. It is often thought 
that coke contains more sulphur than coal, but that is not 
so, as has been already pointed out. The error has arisen 



SOLID PREPARED FUELS 



115 



from the fact that the other products of combustion being 
odourless, the sulphur dioxide produced by the combustion 
is more readily detected. 

Briquettes. — Within the last few years fuel-blocks, or 
briquettes, have come largely into use. They are usually 
made of fine coal or other combustible material, cemented 
together by some cement. The combustible material is 
nearly always coal, but saw-dust, spent-tan, peat, and other 
materials have been suggested. The cementing material is 
usually pitch, but farina (starch), gelatinous matter obtained 
by boiling seaweed, dextrine, molasses, clay, Portland cement, 
lime, and plaster of Paris have all been patented for the 
purpose. The only materials in practical use are coal, coke 
dust, and pitch. 

The variety of apparatus invented for making the blocks 
is probably even greater than that of the materials used. 

The briquettes are usually made up into rectangular 
blocks weighing about 4f to 9 lb., or into small egg-shaped 
lumps. The following analyses will indicate the nature of 
the commercial briquettes : 





1. 


2. 


3. 


4. 


Volatile matter . 


27-67 


330 


150 


45-85 


Coke 


68-18 


59-4 


84-0 


39-27 


Fixed carbon 


57-48 


56-2 


80-0 


28-93 


Ash 


10-7 


3-2 


40 


10-34 


Moisture .... 


415 


7-60 


10 





1, Govan. 2, Coltness. 3, Welsh (average). 4, Russian, made from charcoal and 
pitch. 

The blocks should be uniform in texture, and should be 
so strong that there is little loss by breakage in transport. 
Such loss should not exceed 5 per cent, though with most 
blocks at present made it is far higher. They should not 
contain more than 5 per cent of moisture and 5 per cent of 
ash. As many blocks absorb water very readily, attempts 
have been made to waterproof them by dipping in molten 
pitch, solution of silicate of soda, or other material ; but 



116 FUEL 

none of the methods have come into general use. The blocks 
should not crumble when heated, though unfortunately many 
varieties do. 

Briquettes have one great advantage over coal : being in 
uniform blocks, they pack easily and into small space. This 
is, however, only the case when they can be stacked by hand, 
and does not apply to cases in which they are loaded in 
bulk, as when delivered into the hold of a ship. In this case 
it is very doubtful whether briquettes would occupy less 
bulk, weight for weight, than coal. The heating power of 
briquettes is about equal to that of the coal from which 
they are produced, the evaporative power being from 8 to 
9 lb., the calorific power about 14,000 B.Th.U. 

Manufacture of Briquettes. — The coal, preferably after 
washing, is either crushed in rolls or broken up by a dis- 
integrator into a coarse powder. If very wet, as when 
sludge is used, it is then allowed to drain, and is dried in 
ovens preferably heated by steam, many forms of drying- 
oven having been designed to deal with the materials 
automatically and at the lowest possible cost. If the coal 
be not well dried a larger proportion of pitch is required to 
bind it. The pitch used is usually that obtained by the 
distillation of blast-furnace and coke-oven tars. It is quite 
hard at ordinary temperatures, but softens at about 170° F. 
The pitch is broken into small pieces and mixed with the 
coal before it is passed to the disintegrator, the pitch and 
coal being supplied in the required proportions by means 
of measuring apparatus or distributors of some kind. The 
finely -powdered mixture is transferred to a pug-mill, which 
consists of a vertical wrought-iron cylinder, 30 inches to 
42 inches in. diameter, and 6 or 8 feet high, containing a 
central shaft which makes from twenty to twenty-five 
revolutions per minute and carries arms designed to turn 
over the paste and force it downwards. This is either 
steam- jacketed or arranged so that steam can be blown into 
it, the paste being in the latter case heated by mixing with 
the steam. The first is caljed the " dry-heat," the second 



SOLID PREPARED FUELS 117 

the " wet-heat " process.. In either case the steam may be 
superheated. " The weight of steam required to heat one 
ton of the mixture to 100° C. is, theoretically, only about 
10 lb., but in practice nearly 100 lb. is used." * The 
presence of a small quantity of moisture (3 to 5 per cent) 
in the coal is essential, but the " wet-heat " process is apt 
to introduce too much, unless the steam be superheated 
before use ; but it must not be heated to too high a tem- 
perature (above 200° C.) or pitch may be volatilized. The 
paste is passed from the pug-mill into the compressing 
moulds, where it is subjected to great pressure, and thus 
solidified into blocks. Very many forms of compressing 
machines have been devised. In the simplest form a series 
of moulds is carried on a horizontal rotating table, above 
which is a hydraulic or steam ram. A mould is filled with 
paste, which should not be at a lower temperature than 
about 70° C, from the mixer, and the table is turned so as 
to bring it under the ram, which is then brought down and 
compresses the block ; the ram is then raised, the table 
turned, the block removed from the mould, and the mould 
refilled. The table carries at least three moulds, so that 
while one is being filled another is being pressed and the 
briquette is being removed from the third. In the type of 
machine made by Messrs. Yeadon of Leeds, the moulds are 
cavities in a vertical rotating disc. Each disc has sixteen 
moulds, placed in pairs radially, so that two blocks are 
made at each stroke. The disc being in position, two 
moulds are filled from the mixer, two blocks are com- 
pressed, and two are expelled. A rotation of one-eighth 
of a circle brings two freshly-filled moulds opposite the 
compressing ram, two pressed blocks under the expelling 
ram, and two empty moulds under the spout from the 
mixer — the three operations being simultaneous. As 
the blocks are expelled they push the pair previously 
expelled on to the endless band by which they are carried 
away. 

1 Colquhoun, Mm. Proc. Inst. C.E., cxviii. p. 210 



118 FUEL 

Such a machine will turn out about forty briquettes per 
minute. 

In other forms each mould has its own ram, and in others 
the paste is forced out in a continuous prism, which is cut 
up into pieces of the required size by wires. The briquettes 
as they are removed from the press are soft and friable and 
will not bear handling. They are put on to an endless band 
and conveyed to the store, where they are carefully stacked, 
or they are delivered at once into trucks. 

Cost of Briquette Making. — The cost of manufactur- 
ing at an English works, making 102J tons per day of ten 
hours, with two presses, is given by Colquhoun x as 9s. 7-5d. 
per ton, made up as follows : 

8. d 
1 0-9 



Labour . 

Supplies 

Fuel (for boilers, etc.) 

Materials for briquettes . 

Interest and depreciation 



5-5 

7-2 

7 1-7 

4-2 

9 7-5 



CHAPTER V 

COAL-WASHING 

Object of Coal-washing. — When coal is raised from 
the pit it comes up in pieces of various sizes, the breaking 
of which necessarily produces a large amount of slack or 
smalls. For the market these must be removed either by 
hand-picking or sifting. The small coal usually commands 
a low price, owing to the large quantity of dirt — shale and 
pyrites — which it contains. 

For coke-making, and to a less extent for boiler -firing 
and producer-gas making, it is important that the coal 
should be as free as possible from ash and sulphur. For 
these purposes the coal may be used in a fine state of divi- 
sion, and as the sulphur is mostly present in the form of 

1 Min. Proc. Inst. C.E., cxviii. 



COAL-WASHING 119 

pyrites, which is much heavier than coal, it may be separated 
by methods of washing analogous to those used for the 
dressing of metalliferous ores. 

These methods have now come largely into use, and much 
dross, which would otherwise be quite valueless, has been 
rendered available for coke or briquette making and other 
purposes, while at the same time the larger " coals " have 
been improved by the removal of the smalls and earthy or 
pyritous matter which otherwise would have remained with 
them. 

Principle. — Many forms of apparatus have been devised 
for coal-washing, but they are all based on the same prin- 
ciple, viz. that if particles of the same size, but of different 
weights, be allowed to fall through water the heaviest 
particles will fall most quickly. The rate of fall has been 
investigated by Rittinger, who gives the following formula as 
expressing the rate at which a body will fall in still water : 



V = l-28 VD(d-l), 

where V = velocity in feet per second, D = diameter of holes 
in riddle through which the substance has passed, d = density 
of the substance, and 1-28 a constant deduced from experi- 
mental results. 

If the particles be all of the same density, the falling 
through water will sort them according to their sizes ; and 
if they be all the same size, but of different densities, it will 
separate them according to their density ; whilst if they 
vary both in size and density, they will be separated in a way 
depending on the ratio of the two ; hence for the complete 
separation according to density, good sizing is absolutely 
essential. If the water be in motion instead of at rest, the 
same law will hold good. If the water be flowing, the lighter 
particles, taking longer to fall, will be carried further forward. 
If the water be moving upward, the rate of fall will be 
diminished, and if the upward flow be rightly adjusted the 
lighter particles may be carried upwards whilst the heavier 
fall downwards. 



120 



FUEL 



There are two varieties of coal-washing machines in use 
— those in which the coal is washed by running water ; and 
those in which the water is kept in agitation by a piston 
moving up and down, in a compartment of the washer, as in 
the ordinary Cornish jig, these being therefore called jig 
machines. 

Either type of machine may be applied to the washing of 
coal in lumps, where the larger lumps are to be used for 
domestic or other furnace consump- 
tion, or for washing crushed coal for 
coke-making and similar purposes. 

Trough Machines. — These usually 
consist of a series of inclined troughs, 
each terminating in a grating, through 
which the water and finer materials 
can pass into another trough below, 
the larger pieces passing over the 
grating into a receptacle. 

The coal is supplied to the first 
trough, and is washed down by the 
stream. As it passes along, an at- 
tendant picks out any lumps of shale 
and throws them on one side. The 
coal passes over the end of the grating 
into a receiver, and the finer particles 
FIG.2U.— iiobinson coai-washer. pass through into the next trough. 

From Lock's Mining Machinery. _,, . . ,. .-it • , i • on i 

This trough is provided with rime bars 
which retain the heavier particles of pyrites, whilst the 
lighter coal is carried away into settlers. 

The separation is usually completed in jig machines. 

Robinson Washer. — This consists of a truncated in- 
verted cone, 8 feet diameter at the top, 1 foot 10 inches at 
the bottom, and 6 feet 6 inches deep. A strong shaft is fixed 
in the centre which carries a cross-head, to which are bolted 
wooden arms. To each of these arms are attached three 
vertical iron rods which nearly touch the side of the washer. 
The dross is delivered into the washer in a stream. Water 




COAL-WASHING 121 

is sent in at the bottom and rises upwards through a perfor- 
ated movable bottom plate. The arms are kept in rotation, 
the coal is carried over the top of the washer, and the brasses, 
shale, and other heavy materials sink to the bottom and are 
removed at intervals. 

Jig Machines. — These are much more efficacious than 
simple trough machines. The jigger is a vessel divided into 
two unequal parts by a vertical division reaching nearly to 
the bottom. Across the larger part is a horizontal screen 
perforated with holes. In the smaller part a piston is fitted 
air-tight. As the piston goes down the water is forced up 
through the screen in the other division, and as it rises the 
water returns. The coal is fed into the larger division on 
the top of the screen, and as the water is kept pulsating by 
the motion of the piston the coal is carried away through 
an opening near the top, whilst the heavier material escapes 
through an opening just above the level of the screen. 

For washing fine coal the jigger is a little different in form. 
The screen is provided with openings large enough to allow 
the dirt, brasses, shale, etc., to pass through, and on this 
rests a layer of felspar or other similar material, just too large 
to pass through the holes. As the piston descends the water 
carries the felspar up with it, the lighter coal flows away as 
before by an opening near the top of the chamber, whilst the 
heavier dirt mixing with the felspar settles down ; the dirt 
therefore works gradually downward and ultimately escapes 
through the screen into the space below, from which it is 
removed at intervals. 

The Liihrig Process. — Of all the complete systems of 
coal -washing which have been suggested the one whose 
principle is most largely used is that devised by Mr. Liihrig, 
and it will be sufficient to describe it. 

Assuming that the coal is to be treated as it comes to 
bank, i.e. it is not first crushed, the coal is brought up in 
tubs, which are automatically emptied over screens per- 
forated with 2 -inch holes, so that all coal smaller than that 
passes through. 



122 



FUEL 



The larger coal falls on to endless belts made of steel bars 
with spaces between, so that any small coal formed by 
breakage will pass through, on to another belt below. The 
large coal is picked by hand in the usual way, and at the end 
of the belt is a charging shoot, by which the coal is delivered 
into trucks ; the lower end of this can be lowered so that the 
coal may fall into the truck without being broken. 

Any pieces of shale which are picked out and which seem 
to contain coal are thrown into a hopper, whence they pass 
to a stone-breaker, and thence to the small-coal screens, and 




Fig. 22. — Luhrig's Coal- washing Jig. From Lock's Mining Machinery, z. Pipe for supply 
of water, o, Piston, d, Screen, e, Bars to carry screen. /, Opening for escape of 
coal, b, Valve for removal of sludge, worked by lever a'. 

the refuse which does not contain coal is sent to the waste 
heap. The small coal which passes through the screens falls 
into a hopper of 100 tons capacity, and thence is lifted by an 
elevator to the sizing drum. This is an inclined drum the 
surface of which is perforated with holes so as to sort the 
coal into four sizes : Treble nuts, 2 inches to 1 J inches in 
diameter; double nuts, 1J inches to J inch in diameter; 
single nuts, J inch to T \ inch in diameter ; peas and small, 
below ^ inch ; though of course other sizes may be sub- 
stituted if required. 

Each size is conveyed by a shoot to its own washer. The 
washers are jigs as already described (Fig. 22), the stroke of 
the piston being regulated according to the size of the coal 



COAL-WASHING 



123 



being washed. The screen is not provided with felspar 
pebbles, and the holes are smaller than the holes of the 
sorting screen, so that only the fine dust passes through. 
The coal is carried away by the water over the top of the 
jigger, and the dirt which accumulates on the screen is 
drawn off from an opening just above its surface. 

The washed nuts pass over draining shoots, to which a 
shaking motion is given, to remove water, then to the loading 
hopper and to the trucks. 
As the coal passes down 
the shoots it is sprayed 
with water to remove any 
adhering dust. 

The small coal, as it 
comes from the sizing 
drum, meets the over 
flow water from the nut- 
washers, and is carried to 
a grading box consisting 
of a series of inverted 
pyramids, in which the 
small coal is deposited 
in constantly decreasing 
sizes, the largest settling 
first and the finer in the fig. 23. 
later boxes. 

The mixture of dirt 
and shale from the nut- 
washers is carried by a spiral conveyer to an elevator, and 
thence to rolls, by which it is crushed, and delivered to a 
shoot by which it descends and mixes with the small coal. 

The small coal from the conical settlers passes to a series 
of small jigs (Fig. 23), the screens of which are provided with 
a layer of felspar. The washed coal flows away with the 
washing water to a revolving drum perforated with holes 
eV inch in diameter ; the water and sludge escapes, and the 
coal passes to a hopper for loading. The sludge passes to a 




Liihrig's Fine Coal Jig. From Lock's 
Mining Machinery. I, Water pipe, d, Piston. 
0, Piston-rod, b, c, Screen and its supporting 
bars, x, Layer of felspar pebbles, k, Trap 
for removal of sludge, h, Overflow of coal. 



124 FUEL 

long trough or tank of brickwork or cement running under- 
neath the building ; as the sludge settles it is removed by 
scrapers on endless chains and delivered to a hopper, from 
which it may pass to felspar washers or may be simply dried 
and used. The water is kept in constant circulation and is 
used over and over again. 

The plant is made to treat from 1000 to 3000 tons of coal 
per day. 

Other Types of Coal-washing Plant. — Other and 
more modern systems of coal-washing plant that call for 
mention — it would lead us too far to describe them — are the 
Coppee, Baum, the Draper, the Blackett, and the Hoyle 
systems. The froth flotation process, used very largely in 
America for the purification of minerals, can also be used 
with advantage for separating the gangue from very small 
coal ; in this process about a pound of oil per ton of coal is 
required to assist aeration, and it is necessary to disintegrate 
the coal so as to allow it to pass through a screen of one- 
tenth inch mesh. 

Results of the Washing. — When this process is used, 
coal can be utilized containing so much shale that it would 
otherwise be quite useless, and all the coal is very much 
improved. Less time need be spent in picking in the mine, 
and this alone would lead to considerable saving. At one 
colliery about 5400 tons of coal per year were thrown on one 
side as containing too much shale for use. By the Liihrig 
process this was treated and yielded 4428 tons of marketable 
coal ; and in addition to other saving, about 700 tons of 
pyrites, containing 40 per cent of sulphur, was obtained and 
sold for the manufacture of sulphuric acid. The wetting of 
the coal is sometimes a disadvantage, for example, for gas- 
making. 

The percentage of ash and sulphur is very much reduced, 
thus greatly increasing the value of the coal, as the following 
examples will show : 

[Table 



COAL-WASHING 



125 



Colliery. 


Capacity of 
Plant per day. 


Ash. 


Unwashed. 


Washed. 


Aston Hall Colliery . 
Rosehall ; 

Bardykes 

Motherwell 


1000 
800 
800 

1500 


21 
20 
22 





For coke and briquette making, washing is . almost 
essential, if a good fuel is to be obtained. 

The following tests, made at Ellenborough Colliery, near 
Maryport, will give some idea of the results obtainable : 





Slack 

before 

Washing. 


Pearl 

Coal 

Air-dried, 

fViV 


Sludge, 
tVO. 


Coke 
from 
Pearl , 
Coal. 


Clean Pieces of 
Coal Picked. 


Sp. Gr. 


Ash. 


Water . 
Coke . 
Fixed carbon 
Volatile 
Ash 
Sulphur 


5-24 
65-27 
42-86 
29-49 
22-41 

1-69 


4-92 

4-48 
111 


11-90 


8-92 
1-28 


1-292 
1-255 
1-256 


3-44 
1-60 
1-80 





1. 

Small coal 

before 
Washing. 


2. 
Mixture of 
Pearl Coal 
and Sludge. 


Pearl Coal. 


Sludge. 


Coke from 
Mixture 2. 


Sulphur . 
Ash . 


1-35 
13-78 


•85 
4-14 


2-78 


11-60 


•99 
6-59 



Coal in final dirt, 2-84 per cent. 






126 



FUEL 



CHAPTER VI 



LIQUID FUELS 



Natural Oils. — Natural oils or petroleums are found in 
many parts of the world and are now a most important 
source of thermal energy. The principal oil-producing 
countries are : United States, Russia, Mexico, Dutch East 
Indies, India, Galicia, Japan, Roumania, Peru, Trinidad, 
Argentina, Egypt, and Germany. 

The natural oils vary very mucn in colour, consistency, 
smell, and other properties ; some are thin, limpid, and of 
pale colour, others are dark coloured, and of nearly the 
consistency of treacle. 

The petroleum from the oil-wells of America is mainly 
composed of saturated hydrocarbons of the paraffin series 
(C n H 2n+2 ), sometimes containing oxidized bodies, the higher 
solid paraffins being dissolved in the lighter liquid members 
of the series. The oils always contain members of the olefine 
(C n H 2n ) and the benzene (C n H. 2a _ e ) series, and in some cases 
also sulphur, whilst the Russian petroleum consists much 
more largely of olefines. The following analyses by M. 
Goulishambaroff may be taken as examples : 





Sp. 
Gr. 


Composition. 


CP. 

British Units. 


Evapora- 
tive Power. 


C. 


H. 


0. 


Russian crude) Light 
petroleum J Heavy 

Pennsylvanian crude 
heavy oil . 


•884 
•938 

•886 


86-3 
86-6 

84-9 


13-6 
12-3 

13-7 


•1 
11 

1-4 


22630 
19440 

19210 


17-4 
16-4 



These figures must only be regarded as examples, as the 
actual composition of the oils varies very much. 

World's Output of Petroleum. — The following table 
gives a survey of the approximate quantities of crude natural 



COAL-WASHING 



127 



oil produced by the principal oil-bearing fields of the world 
for the year 1917. 



United States . 

Russia 

Mexico 

Dutch East Indies 

India 

Galicia 

Japan and Formosa 

Roumania 

Peru 

Trinidad . 

Argentina 

Egypt . 

Germany. 

Total about 



Million Tons. 


Percentage 
of total. 


48 


67 


10 


14 


80 


11 


1-9 


2-6 


1-2 


1-7 


0-85 


1-2 


0-41 


0-6 


0-37 


0-5 


0-36 


0-5 


0-23 


0-3 


016 


0-2 


0-14 


0-2 


014 


0-2 



72 



100-0 



Millions of Gallons. 


1913. 


1918. 


11 




157 


148 


68 


102 


66 


41 


95 


842 


101 


193 


include the 


enormous 



Imports of Petroleum Products. — The following are 
the approximate quantities of petroleum products imported 
into the United Kingdom for the years 1913 and 1918 : 



Crude Petroleum 
Lamp Oil 
Lubricating Oil 
Gas Oil (Solar Oil) 
Fuel Oil . 
Motor Spirit 

The figures for fuel oil for 1918 
quantities used by the Navy. 

Occurrence of Petroleum. — Petroleum usually occurs 
impregnating porous sandstone or limestone rocks, these 
rocks sometimes holding as much as one-eighth their bulk of 
oil. " This means 1 \ inches of oil to the vertical foot of rock, 
equal to 1000 barrels per acre. Carll states that the oil rock 
of the Venango * is from 30 to 50 feet thick in the third sand, 
and 15 to 30 feet in the other sands ; assuming only 15 feet 
of good rock, this means 15,000 barrels per acre, or nearly 
10,000,000 barrels per square mile." 

The oil is obtained by means of wells sunk down to the oil- 

1 Venango County in Pennsylvania. 



128 FUEL 

bearing strata, the oil being raised by pumping or otherwise. 
In many cases the oil flows from the bore-hole without the 
need for pumping, it having been confined in a synclinal 
trough or by a fault, so that the pressure of the mass of oil 
alone is sufficient to force it out of the opening, and thus to 
produce an oil spring or flowing well, 

" Many facts support the theory that the oil-producing 
sands lie in pockets or patches surrounded by impervious 
rock, so that each pool forms a separate, and to a very large 
extent independent reservoir of oil." 

Petroleum is not confined to rocks of any particular age, 
nor does it occur on any special geological horizon. The 
Pennsylvanian deposits are mainly in Devonian and to a less 
extent in carboniferous rocks. Part of those of Ohio and 
those of Kentucky are in Silurian limestone. The oil of the 
Florence field (Colorado) is in the cretaceous, the oil-fields of 
California and also those of Eastern Europe are in tertiary 
rocks. Oil has even been found in volcanic rocks, though 
probably as an infiltration from saturated rock masses. 

Origin of Petroleum. — Several theories have been ad- 
vanced as to the origin of mineral oils, but up to the present 
the matter cannot be regarded as settled. It has been 
suggested that they might be due to the action of water on 
certain carbides, such for instance as calcium carbide, which 
under ordinary pressures yields acetylene, and which there- 
fore under other conditions it is thought might yield other 
hydrocarbons. 

The general view is that it is of organic origin, and derived 
either from plant or animal remains. Several eminent geo- 
logists have held that the oils have resulted from the distilla- 
tion by heat of beds of coal or similar materials ; but against 
this may be put the fact that the beds in which the oil occurs 
show no sign of the action of heat. Another view, first pro- 
pounded by Dr. T. Sterry Hunt, is that the oils have been 
formed from vegetable remains, but by a process different 
from that which produced coal. He held that vegetable 
matter may decay in two ways: (1) in presence of air and 



LIQUID FUELS 129 

water, when the hydrogen and carbon will be partially elimi- 
nated, and a solid residue of coal will be left ; or (2) in the 
absence of air and moisture, when the tendency would be to 
form saturated hydrocarbons. 

More recently it has been urged that mineral oils are pro- 
bably derived from animal remains, and C. Engler asserts that 
any animal fat can be converted into petroleum by distilla- 
tion under pressure. 

Crude petroleum is usually subjected to fractional dis- 
tillation before use, and only the heavier portions are used 
for fuel. 

Prepared Oils. — The prepared oils used for fuel are 
obtained by the distillation of — 

1. Crude mineral oil. 

2. Oil shales. 

3. Blast-furnace tar and similar materials. 

Distilled Petroleums. — The crude Pennsylvanian petro- 
leum is distilled in iron retorts heated by a fire, and the pro- 
ducts of distillation are passed through condensers which 
usually consist of straight lengths of pipe connected by return 
bends and contained in a large vessel of water. The distillate 
is turned into separate vessels as the temperature rises, 
so that four distinct distillates are usually obtained — light 
and heavy naphthas, and light and heavy oils — the division 
between the four varying in different works. 

The yield is : naphtha 8 per cent to 20 per cent, oils 76 
per cent to 78 per cent, residue 5 to 9 per cent, and loss, i.e. 
permanent gases, about 5 per cent. 

The heavy oil may be used as fuel direct, or it may be 
subjected to further fractional distillation so as to prepare 
different grades of burning and lubricating oils. 

The custom at most of the Baku works is to distil off 
about 30 per cent of the crude oil, and to use the residue, 
known as petroleum refuse, as fuel. The results obtained 
being : light petroleum 5 to 6 per cent, burning oil (1), 
(kerosene) 27 to 33 per cent, burning oil (2), (solar oil) 5 to 
6 per cent, residues 50 to 60 per cent. 

(D107) K 



130 



FUEL 



Shale Oils. — These oils are largely obtained by the dis- 
tillation of bituminous shales. The nature of the shales can 
be seen from the following figures : 





1. 


2. 


Volatile matter .... 

Coke 

Fixed carbon .... 
Ash 


34-96 

65-04 

7-44 

57-60 


13-5 

86-5 

2-5 

840 



1, Broxburn. 2, West Wemysa (Fife). 

The shale is distilled in vertical retorts, into which steam 
is blown. The products of distillation are passed through 
condensers, which consist of several series of vertical tubes 
exposed to the air. The products, separated according to 
their condensibility, consist of crude oil, sp. gr. -890—896; 
light oil, -790--805 ; naphtha, -730, and large quantities of 
permanent gases which are washed for recovery of ammonia 
and light oils before being used as fuel. The oils are further 
refined by fractional distillation and treatment with acids 
and alkalies, and separated into the various grades of illum- 
inating and lubricating oils, petroleum naphthas, and 
paraffin wax. About 4 million tons of oil shale are annually 
subjected to destructive distillation in the south of Scotland, 
producing about 400,000 tons or about 100,000,000 gallons 
of crude oil. 

Oil from Blast-furnace Tar. — The tar obtained from 
the waste gases of blast-furnaces fed with coal is the source of 
a considerable quantity of oil suitable for use as a fuel. Each 
ton of coal consumed yields about 30 gallons of tar ; this is 
distilled in wagon-boiler retorts, or special stills, and each 
100 parts yields about 50 parts of water, 20 parts of oil, and 
30 parts of pitch. The oils obtained are divided into two 
portions — heavy or creosote oils which have a specific gravity 
of -960 to -980, and light oils or spirit, having a specific gravity 
of '900 to *901. The heavy oils are those which are used as 
fuels. 



LIQUID FUELS 131 

Oils as Fuels. — Oil fuels have many advantages over 
solids, among which the following may be noted : 

1. Reduction of weight by about 40 per cent. 

2. Reduction of bulk by about 35 per cent. 

3. Reduction of number of stokers required in about the 
ratio 4:1. 

4. Very small proportion of ash in the fuel. 

5. Prompt kindling of fires and consequent early attain- 
ment of the maximum temperature of the furnaces. 

6. The fire can be extinguished at any moment. 

7. Uniformity of combustion and therefore of heating 
power. 

8. Reduction of discomfort of loading fuel, clinkering 
fires, and stoking. 

Against these advantages may be set the disadvantages of : 

1. Danger of explosion. 

2. Loss of fuel by evaporation. 

3. Unpleasant odours. 

The first and second disadvantages are eliminated by a 
proper choice of the oil whereby a high boiling oil with high 
flash-point is specified. 

Future of Oil Fuel. — In spite of the fact that before 
the war a therm (100,000 British Thermal Units) cost two or 
three times as much in the form of oil as it did in the form of 
coal, and that since then the discrepancy has still further 
increased, there have been immense developments in the use 
of oil fuel, more especially for the Navy and Atlantic liners. 
For the Navy, speed of renewal of fuel, convenience of taking 
supplies of oil from oil-tankers at sea, increased radius of 
action, increased speed, and reduction of hands are advan- 
tages of paramount importance. 

Atlantic liners, too, find it to their advantage to be able 
to shorten considerably the time required for a double trip, 
and to increase their passenger accommodation by the 
reduction of the crew. 

When oil engines are used, the increased thermal 
efficiency of internal combustion may more than counter- 



132 



FUEL 



balance the additional cost of heat units supplied in liquid 
form. 

As regards light oils, like petrol, gasoline, benzol, and 
alcohol, the demand for motor vehicles of all kinds, for motor 
boats, for aeroplanes and airships is ever on the increase, 
with the result that all possible sources of supply are being 
sought out, although it is only a few years since oil refiners in 
the foreign oil-fields were finding that the production of light 
spirit very much more than satisfied all demands. Of late 
years vast quantities of motor spirit — as much as 100,000,000 
gallons per annum — have been obtained by washing certain 
grades of natural gas with heavy oil in a similar way to that 
employed for coke-oven gas. Methylated spirit and mixtures 
of methylated spirit with benzole have also been brought into 
use as motor spirit. 

There can be little doubt that in the future oil fuel will 
be more largely used as its advantages come to be recognized. 
That it will supersede coal, either used directly or through 
the form of gas, is not at all likely, but there are very many 
purposes for which its use will be most advantageous. 

The following table will show the relative heating values 
of petroleum and coal : 



Fuel. 


Sp. Gr. 


Composition. 


C.P. 


E.P. 




32° F. 


c. 


H. 


0. 


S. 


B.Th.U. 


Water 
at 212° 


Pennsylvania heavy- 
















crude oil . 


•886 


84-9 


13-7 


1-4 




20740 


21-48 


Caucasian light crude 
















oil ... 


•884 


86-3 


13-6 


•1 




22030 


22-79 


Caucasian heavy crude 
















oil . . . . 


•938 


86-6 


12-3 


11 




20850 


17-3 


Mexican fuel oil . 


•965 


81-5 


11-2 


3-5 


3-7 


18450 


191 


Petroleum refuse 


•928 


87-1 


11-7 


1-2 


. . 


19830 


171 


Good English coal, 
















average of 98 samples 


1-380 


80-0 


50 


80 


1-25 


14110 


1216 



Essential Qualities in a Fuel Oil. — 1. The water 
content should be as low as possible, certainly not more 
than 2 per cent. Petroleum is easily obtained in a 
dehydrated condition, as it is the practice to distil off the 



LIQUID FUELS 133 

light fractions for motor spirit, the middle fractions for 
lamp and lubricating oil, leaving the fuel oil behind, the 
water being also distilled off in the process. It sometimes 
happens that live steam is used to warm the thick oil to 
make it flow more readily, and there is then a great danger 
of emulsifying the oil with the condensed steam, and samples 
may be found containing as much as 25 per cent of water. 
The chief danger in the presence of water is the extinguish- 
ing of the burner flames. The bulk of the water may be 
separated out in the storage vessels by heating up the 
emulsion to at least 70° C, and allowing the whole mass 
to remain hot for a day or two. 

Heavy coal-tar, carburetted water-gas tar, and producer- 
gas tar are particularly troublesome to dehydrate once 
they have got into the state of emulsion. It is not un- 
common to find such tars containing 50 per cent of water, 
a quantity which naturally detracts greatly from their 
value. Various types of dehydrating plants are in use, 
the more convenient designs being continuous in their 
action. A good coal-tar should contain not more than 
4 or 5 per cent of water, before dehydrating, if made and 
stored under proper conditions. 

2. Freedom from solid matter is another essential. Coal- 
tar generally contains a considerable amount of " free 
carbon " — solid matter insoluble in benzene or petrol. 
This is usually for the most part very finely divided, being 
the result of " cracking " the heavier tar oils in the process 
of carbonization. The content varies from about 3 per 
cent in vertical retort tar to 30 per cent in some tars from 
horizontal retorts and coke ovens. Not only is free carbon 
present in most tars, but also grit consisting of coal, coke, or 
ash, and it is this grit that is most objectionable, as it is 
very liable to choke the fine orifices of the burners unless 
special filtering arrangements are installed. 

3. The flash-point must be sufficiently high so as to 
avoid as much as possible the risk of the accumulation of 
vapours which would form an explosive mixture with air. 



134 FUEL 

For safety it should not be less than 140° F. This condi- 
tion usually necessitates the elimination by distillation of 
the light fractions. 

4. The viscosity should not be too high at ordinary 
temperatures, otherwise the rate of loading and unloading 
will be seriously retarded. The British Admiralty (1913) 
specifies a viscosity of not more than 2000 seconds for an 
outflow of 50 c.c. at a temperature of 32° F., as determined 
by Sir Boverton Redwood's Standard Viscometer (Admiralty 
type for testing fuel oils). 

Creosote oil containing naphthalene has a remarkable 
thinning effect on thick tars and may sometimes be used 
with advantage. 

5. The proportion of sulphur in the oil should not be 
excessive. It is difficult to define the amount that may 
be considered excessive. The British Admiralty specifies 
a limit of 3 per cent, whereas the United States Bureau of 
Mines would impose a limit of 1 per cent. Where the 
waste gases remain hot there is little danger of corrosion 
from sulphur acid gases, and it would seem possible to 
consume with impunity fuel oils having a high content 
of sulphur. Pennsylvanian and Russian petroleum contain 
not more than 1 per cent and Texas petroleum 2 per cent. 
Mexican fuel oil contains 3J per cent, and Norfolk shale 
oils as much as 6 or 7 per cent, of sulphur. 

6. It is necessary sometimes to specify freedom from 
acid, seeing that sulphuric acid is used in the refining of 
oils. This, according to the British Admiralty specification, 
should not exceed 0-05 per cent calculated as oleic acid. 

7. The specific gravity will of course vary with the 
nature of the oil fuel, ranging from 0-85 for shale oil to 1-2 
for heavy coal-tar, as measured at 60° F. 

The coefficient of expansion (ratio of the increase in 
volume for one degree to the original volume) must be 
allowed for in determining tonnage by volume measurement. 
For coal-tar this is 000032, for water-gas tar 000035, and 
for petroleum 0- 0003 8 per degree Fahrenheit. 



LIQUID FUELS 135 

8. The calorific value on the dry basis varies from 
16,000 to 22,000 B.Th.U. per lb. It is lowest where there 
is a large amount of oxygen compounds or much free carbon, 
as in certain coal-tars, and highest where the oils consist 
of naphthenes or other unsaturated hydrocarbons and little 
oxygen. 

The above conditions are sufficiently wide to embrace 
almost all heavy oils and tars that do not contain too much 
water or grit. In fact the term " fuel oil " is rather mis- 
leading, seeing that the material generally supplied as fuel 
for shipping more nearly resembles thick tar than oil. 

Oil Fuel for Internal Combustion Engines. — The 
oils generally used for engines of the Diesel or semi-Diesel 
type are the middle oils, too heavy for motor spirit and 
unnecessarily light for furnace work. There is no definite 
specification for suitable oils. Moisture and carbon and 
grit must naturally be excluded as far as possible. The 
flash-point will be over 72° F. and no special precautions 
will therefore be necessary in storage and distribution. The 
sources from which the oil can be drawn are many and 
wide. Even coal-tar made in vertical retorts and low in 
free carbon content has been used with success in Diesel 
engines. Nevertheless, uniformity of quality is essential. 
Diesel oils have a low vapour tension and can only vaporize 
sufficiently to form an explosive mixture with air in a hot 
cylinder. The necessary temperature is attained by high 
compression of the air used, and the degree of compression 
will vary with the nature of the oil. Formerly illuminating 
oils, such as paraffin oil, were chiefly in demand, but there 
is now a tendency to utilize cheaper heavy oils of all kinds. 
The consumption is from 0-4 lb. upwards per B.H.P. hour. 

Motor Spirit. — For high - speed internal combustion 
engines, suitable for quick starting, either a combustible 
gas or a volatile oil readily producing a combustible vapour 
is employed. The principal light spirits now in use for 
this purpose are petrol, benzol, and alcohol. 

Petrol. — This forms by far the largest bulk of light 



136 FUEL 

spirit consumed by motor vehicles. It consists of the 
more volatile, or low boiling, constituents of natural 
petroleum or of the heavier vapours occurring in natural 
gas. It is recovered from petroleum by a process of frac- 
tional distillation or from the natural gas by oil washing, 
stripping, and distillation. It contains principally paraffin 
hydrocarbons of the general formula, CnH. 2 n + 2, such as 



Pentane, C 6 H,„ sp. gr. 


0-64, 


boiling at 37° C. 


Hexane, C 6 H 14 , „ „ 


0-67 


6Q° 


Heptane, C 7 H 16 , „ „ 


0-69 


» » 98 „ 


Octane, C 8 H 18 , „ „ 


0-71 


n » 125° „ 


Nonane, C 9 H ao , „ „ 


0-73 


» »» 150 „ 



also naphthenes of the general formula, CriK 2 n, such as 
hexamethylene, C 6 H 12 , and other methylene hydrocarbons. 

Ordinary petrol distils completely over between 60° 
and 170° C, the bulk of it boiling between 90° and 110°. 
More reliance is to be placed on petrol which is lighter or 
has the lower boiling range, especially for aeroplane work 
where the atmospheric temperatures may be very low. 

The specific gravity varies between 0-68 and 0-72. The 
average composition is roughly 85 per cent of carbon and 
15 per cent of hydrogen. The gross calorific value averages 
about 20,100 and the net value 18,500 B.Th.U. per lb. 
The sulphur content is so small as to be negligible. 

Benzol. — This is known to the chemist in the pure 
state as benzene, C 6 H 6 . It is the first member of what 
is called the aromatic series of hydrocarbons. In commercial 
benzol it is accompanied by the higher homologues, toluene, 
C 7 H 8 , and xylene, C 8 H 10 . Its principal sources are coal- 
gas, coal-tar, and certain petroleums (Borneo, Rumania). 

The specification issued by the Automobile Association 
(1919) is as follows : 

1. Specific gravity, 0-87-0-88. 

2. Flask distillation, not less than 75 per cent by volume at 100° C, 
not less than 90 per cent at 120° C, and not less than 100 per cent at 
125° C. 

3. Sulphur not to exceed 0*4 per cent. 

4. Entirely free from water. 

5. Colour — water-white. 



LIQUID FUELS 137 

6. 90 c.c. of the benzol shaken with 10 c.c. of 90 per cent sulphuric 
acid for five minutes shall not give more than a light brown colour to 
the acid layer. 

7. Entirely free from acids, alkalis, and sulphuretted hydrogen. 

8. Shall not freeze at 7° C. 

The calorific value is usually about 17,800 B.Th.U. per lb. 
gross and 17,100 net. Although these values are lower 
than those of petrol per lb. the specific gravity is so much 
higher that the net calorific value of a gallon of benzol is 
about 14 per cent higher than that of a gallon of petrol. 

Benzol has the disadvantage of freezing easily. Pure 
benzene freezes at 6° C. (43° F.). The freezing point, how- 
ever, is lowered by the addition of small quantities of petrol 
or alcohol. It does not start the engine so easily as petrol, 
and requires considerably more air for combustion. 

Alcohol, C 2 H 5 OH. — The importance of alcohol as a 
fuel will necessarily be more and more recognized as the 
resources of coal and oil become exhausted. It is the 
only liquid fuel of any account which can be artificially pro- 
duced from the earth's soil. Potatoes and other foodstuffs 
containing starch or sugar yield large quantities of alcohol 
by a process of fermentation and subsequent distillation. 
Cost of production and Excise restrictions at present limit 
its extended use. 

New processes of manufacture from cheaper materials, 
such as wood-pulp or even peat, are being developed and 
give promise of a great future for alcohol as a motor spirit. 

Alcohol has a comparatively low calorific value — 90 per 
cent alcohol giving 11,100 gross and 10,100 net per lb. — 
but it gives a high thermal efficiency owing to the high 
compressions that may be used without fear of pre-ignition. 
It is less dangerous than petrol or benzene for storage as 
its flash-point is higher. It has the advantage of being 
miscible with benzene. The explosive range is greater than 
that of benzene vapour or petrol vapour, and as the rate 
of propagation of the flame is slower there is a greater 
latitude and also steadier pressure in the working of the 
engine. 



138 



FUEL 



The following comparison of the three spirits in tabular 
form brings out the chief points of difference : 





Petrol. 


Benzol. 


Alcohol. 


Specific gravity 


0-72 


0-88 


0-82 


Boiling points .... 


60° -170° C. 


80° -125° C. 


80°- 110° C. 


Freezing point 


Below- 100° C. 


Below 6° C. 


Below -100° C. 


Calorific value — 








B.Th.U. per lb. gross . 


20,100 


17,800 


11,100 (90%) 


B.Th.TJ. per lb. net . 


18,500 


17,100 


10,100 „ 


B.Th.U. per gallon gross . 


144,700 


156,600 


91,000 „ 


B.Th.U. per gallon net 


133,200 


150,500 


82,800 „ 


Theoretical air for combustion 








cubic feet per gallon . 


1440 


1560 


940 


Explosive range — 








per cent of vapour 


1-5* 


2f-6i 


4-13* 


Safe compression — 








lbs. per square inch . 


Up to 70 


Up to 80 


Up to 200 


Heat of evaporation (calories) 


85 


93 


237 


Specific heat .... 


0-46 


0-42 


0-65 


Co-efficient of expansion — 








per degree C. 


00008 


00014 


00011 



CHAPTER VII 



GASEOUS FUEL 



Natural Gas. — In certain localities considerable quanti- 
ties of combustible gases are given off from the earth, and in 
Pennsylvania these have been largely used as fuel. In many 
cases in boring for oil vast reservoirs of gas, evidently under 
great pressure, were struck, which therefore escaped with 
great force. It was, however, some years before any one 
thought of utilizing this gas for fuel, though its heating power 
was well known. The first attempt was made in 1879, when 
pipes were laid to carry the gas from one of the vents to an 
ironworks near Pittsburg, where it was used for puddling. 

The amount of gas escaping is very large. It was estimated 
that in 1885 there were 50 gas wells at work, yielding in the 
aggregate about 100,000,000 cubic feet of gas per day. The 
pressure at which the gas escapes varies much, and at Pitts- 
burg is from 100 to 200 lb. on the square inch. The gas 
region covers a very large area, and is very intimately con- 



GASEOUS FUEL 



139 



nected with the oil-bearing region, the two indeed being 
geologically identical, though the gas-field seems to cover a 
larger area. Gas very generally accompanies natural oils, 
but occurs also in coal districts. 

Composition of Natural Gas. — Natural gas consists al- 
most entirely of marsh-gas (CH 4 ) and hydrogen, and has a 
very high calorific power. The following analyses (Ford, 
quoted in Mills and Rowan's Fuel) will give an idea of the 
composition of the gas : 



Carbonic acid, C0 2 

Carbonic oxide, CO 

Oxygen . 

Ethylene (olefiant gas) 

Ethane . 

Marsh -gas 

Hydrogen 

Nitrogen. 



•8 
10 
11 

•7 

3-6 

72-18 

20-62 



•6 

•8 

•8 

•98 

5-5 

65-25 

26-12 



•58 

•78 

•98 

7-92 

60-70 

29-03 



10 

210 

•8 
5-20 

57-85 
9-64 

23-41 



To calculate the calorific power of the gas we may assume 
an average composition and multiply by the respective 
calorific values of the constituents (in B.Th.U. (gross) per 
cubic foot) : 



Carbon dioxide 






0-006 






Carbon monoxide 






0-006 x 


320 = 


19 


Oxygen 






0-008 






Ethylene 






0-010 x 


1580 = 


= 15-8 


Ethane 






0-050 x 


1650 = 


= 82-5 


Methane 






0-670 x 


998 = 


= 668-7 


Hydrogen . 






. 0-220 x 


321 = 


= 70-6 


Nitrogen 






0030 







1000 



839-5 



As 1000 cubic feet of gas of the above composition weigh 
almost exactly 38 lb., the calorific value per lb. is 22,090 
B.Th.U. (gross), a much higher value than the best coal or 
coke. 

The gas is practically free from sulphur. On strong 
heating it splits up and deposits a hard glassy coke, so that 
it cannot be used with regenerators in the Siemens furnace. 



140 FUEL 

Artificial Gas. — Many forms of gas have been made at 
various times for lighting and heating purposes. Those 
which are at present in use are — 

1. Coal-gas. 

2. Producer-gas. 

3. Water-gas. 

4. Oil-gas. 

Coal-gas. — This is the gas obtained by distilling coal in 
closed retorts. Its principal uses are for domestic lighting, 
heating, and cooking. It has a very high calorific power, 
and is an excellent fuel. It is too expensive for general 
furnace use, but is employed with success in many minor 
operations where only a small quantity is required, and 
its cost is only of secondary importance. In recent years 
town-gas has been extensively used in industrial centres for 
metal melting and annealing, for glass-working and various 
other purposes. Some idea of the extent to which town- 
gas is now consumed can be gained from the following data 
published by Dr. C. M. Walter (Gas Journal, October 27, 
1920): For the year 1912-13 the total volume of gas 
supplied for industrial heating (that is, apart from house- 
hold gas-fires and cookers) in the city of Birmingham area 
was 609,000,000 cubic feet, being the gas yield from 50,000 
tons of coal. For the year 1918-19 the gas supplied for 
industrial heating was 2,522,000,000 cubic feet, the yield 
from 200,000 tons of coal. In the former case it represented 
6-7 per cent of the total output of town-gas, in the latter 
21-0 per cent. It is most conveniently supplied in special 
mains under a pressure of about 12 lb. per square inch, and 
the furnaces may work directly off high-pressure gas jets 
inducing their own air supply, or the gas may be used 
at ordinary pressure with or without air blast. The 
amount of gas yielded by coal varies from 10,000 to 14,000 
cubic feet per ton. The gas to be used for lighting purposes 
is carefully purified from sulphuretted hydrogen. Formerly 
qarbon dioxide and sulphur compounds were also almost 



GASEOUS FUEL 



141 



entirely eliminated, but the advent of the incandescent 
burner rendered this course less necessary. The pre-war cost 
of gas varied in this country, say, from Is. to 5s. per 1000 
cubic feet, the usual cost being probably about 2s. 6d. The 
luminosity of the flame of coal-gas gives it an advantage for 
many purposes over those gases which burn with a non- 
luminous flame. The following analyses will give an idea as 
to the composition of coal-, cannel-, and oil-gas : 



Carbon dioxide 

Oxygen .... 

Unsaturated hydrocarbons 

Carbon monoxide . 

Methane .... 

Hydrogen 

Nitrogen .... 



1, An average lime-purified coal 

2, „ „ oxide- 
lime- 



1. 


2. 


3. 


4. 


0-8 


2-5 


0-8 


0-5 


0-7 


1 


0-7 




4-5 


3 


15 


35 * 


7 


8 


6-5 


0-5 


35 


25-5 


35 


43 


45 


46 


35 


20 


7 


14 


7 


1 



oil-gas. 



■gas of year 1900. 

„ 1920. 

cannel-gas ,, 1900. 



We may calculate the gross calorific value of No. 2 as 
follows, taking the unsaturated hydrocarbons C m H n as 
having a value of 2320 B.Th.U. per cubic foot : — 



CmHn 


. 0-03 


X 


2320 


= 


69-6 


CO 


. 0-08 


X 


320 


= 


25-6 


CH 4 


. 0-255 


X 


998 


= 


254-5 


H. 


. 0-46 


X 


321 


= 


147-7 



497-4 

Under the new Gas Regulation Act (August 1920), town- 
gas is to be sold on a basis of thermal units, gross value, the 
unit of sale being called the therm, which is standardized as 
100,000 B.Th.U., gross. Assuming a gas of 500 B.Th.U. 
to cost 3s. 4d. per 1000 cubic feet, the price per therm is 8d. 

A coal having a calorific value of 12,500 B.Th.U. per lb., 
and costing 37s. 4d. per ton, represents a cost per therm of 
l-6d. or one-fifth of the above figure. In spite of this 

* Includes Ethane 



142 FUEL 

difference there are many cases where town-gas is able to 
displace coal. 

Producer-gas. — When air is blown through red-hot 
charcoal or coke, combination takes place, and since the 
temperature is high and the carbon is in large excess, carbon 
monoxide is produced, which makes the resulting gas com- 
bustible, C+0=CO. Since air contains by volume 21 per 
cent of oxygen and 79 per cent of nitrogen, and since the 
carbon monoxide produced occupies twice the volume of the 
oxygen which is consumed, the gas thus obtained would 
contain about 34-7 per cent of carbon monoxide. Such a 
gas, though combustible, has naturally a very low calorific 
power, and whilst many attempts were made to utilize it, 
they were unsuccessful until the introduction of the Siemens 
regenerative furnace. Gas from blast-furnaces, which, as 
will be seen later, is of much the same character, had been 
utilized for various purposes as far back as 1840. 

This gas may be called simple producer-gas to distinguish 
it from other forms of gas which are produced by similar 
means but enriched in various ways, and which may there- 
fore be called enriched producer -gas. The principal methods 
of enriching are by blowing in steam or water, which under- 
goes decomposition, the liberated hydrogen and carbon 
monoxide enriching the gas, C + H 2 = CO + 2H ; and by 
using coal instead of coke, in which case 
the volatile products of distillation mix 
with the gas. 

The Bischof Producer. — The first 
attempt to manufacture producer-gas for 
furnace use was made by Bischof in 1839. 
The producer consisted of a cylindrical 
brick chamber having a capacity of about 
150 cubic feet ; at the bottom of which 
was a grate, on which rested the column 

Bischof Gas Producer. Q f f ue j r^ f ue [ uge( J wag p ea t 5 which 

was charged at the top, and air was admitted beneath the 
grate. Round the body of the producer were arranged holes 




GASEOUS FUEL 143 

through which the working could be observed, and the gas 
was drawn off at the side near the top. No blast was used, 
but the air current was kept up by chimney draught. 

Since that time an enormous number of gas producers 
have been invented. 

Classification of Gas Producers. — To arrange a classi- 
fication which will suit all the forms that have been suggested 
is almost impossible. The following, however, includes all 
the more important types : 

1. Producers worked mainly by natural draught, i.e. with 
open hearths. 

a. With fire-bars. 

b. With solid bottom. 

2. Producers worked by blast, usually produced by a 
steam jet. 

a. With fire-bars. 

b. With solid bottom. 

(1) Bottom worked dry. 

(2) With water bottom. 

The Bischof producer, already described, falls under 
class 1, division a. 

The Siemens Producer. — This is the first form of pro- 
ducer that was a commercial success. In the early days of 
the Siemens or open-hearth steel process it was almost 
universally used, and it is still in use, usually with some 
modification, in many steel works. The Siemens regenera- 
tive furnace was invented in 1861, and it is from that time 
that the practical use of producer-gas must be dated. 

One form of this producer suitable for burning non-coking 
slack is thus described by Siemens : "In form it is a rec- 
tangular fire-brick chamber, one side of which, b, is inclined 
at an angle of from 45° to 60°, and is provided with a grate c 
at its foot. The fuel is filled in at the top of the incline A, 
and falls in a thick bed upon the grate. Air is admitted at 
the grate, and as it rises through the ignited mass the car- 
bonic acid first formed by the combustion of oxygen with the 
carbon of the fuel takes up an additional equivalent of 



144 



FUEL 



carbon, forming carbonic oxide, which is diluted by the inert 
nitrogen of the air and by a little unreduced carbonic acid, 
and mixed with the gases and vapours distilled from the raw 
fuel during its gradual descent towards the grate, and is led 
off by the gas flue to the furnace. The ashes and clinkers 
that accumulate on the grate are removed at intervals of 
one or two days. 

" The composition of the gas varies with the nature of the 
fuel and the management of the gas producer. That of the 
gas from the producers at the plate-glass works, St. Gobain, 




Fig. 25. — Siemens Gas Producer. 



France, burning a mixture of f caking coal and J non-caking 

d July 1865 (by 



coal, is as follows by an 


analysis c 


volume) : 




Carbonic oxide „ 


. 23-7 


Hydrogen . 


8-0 


Methane 


2-2 


Carbonic acid 


41 


Nitrogen 


. 61-5 


Oxygen 


•4 



24-2} 

8-2 \ 

2-2 J 

4-2} 

61-2J 



34-6 



65-4 



99-9 

" The trace of oxygen present is no doubt due to careless- 
ness in collecting the gas or to leakage of air into the flue. 
The figures in the second column give the composition of the 
gas, allowance being made for the accidental oxygen." * 

1 Siemens, Collected Works, vol. i. p. 219. 



GASEOUS FUEL 



145 



I 




In all the producers of this type in use now water is 
supplied ; either a steam jet is fixed under the bars or a 
water-spray is projected on to the bars or into the fire. 
Fig. 26 shows a form of this producer at present in use. 

As the air supply depends entirely on the draught pro- 
duced by the ascending current of hot gas, the pressure is 
very small and the combustion is slow, the amount of coal 
consumed being only about 12-13 lb. of coal per square foot 
of grate area per hour. 

The gases leave the producer at a temperature of about 
500° or 600° C. (1000° F.), and being there- 
fore very light they tend to rise, thus 
producing the draught. "It is necessary 
to maintain this pressure through the whole 
length of the gas flue, in order to ensure a 
free supply of gas to the furnaces, and 
to prevent its deterioration in the flue 
through indraught of 
air at crevices in the 
brickwork. The slight 
loss of gas by leakage, 
which results from a 
pressure in the flue, is 
of no moment, as it 
ceases entirely in the 
course of a day or two, 
when the crevices become filled with tar and soot. 

" Where the furnace stands so much higher than the gas 
producer that the flue may be made to rise considerably, the 
required plenum of pressure is at once obtained ; but more 
frequently the furnaces and gas producers are placed nearly 
on the same level, and some special arrangement is necessary 
to maintain the pressure in the flue. The most simple con- 
trivance for this purpose is the * elevated cooling-tube.' The 
hot gas is carried up by a brick stack to a height of eight 
or ten feet above the top of the gas producer, and is led 
through a horizontal sheet-iron cooling-tube of not less than 




Fig. 26.— Siemens Gas Producer. 



146 FUEL 

60 square feet of surface per gas producer, from which it 
passes down either directly to the furnace or into an under- 
ground flue. 

" The gas rising from the producer at a temperature of 
about 1100° F. is cooled as it passes along the overhead tube, 
and the descending column is consequently denser and 
heavier than the ascending column of the same length, and 
continually overbalances it. The system forms, in fact, a 
syphon, in which the two limbs are of equal length, but one 
is filled with a heavier liquid than the other. The height of 
cooling-tube required to produce as great a pressure in the 
flue as would be obtained by placing the gas producers say 
ten feet deeper in the ground, may be readily calculated. 
The temperature of the gas as it rises from the producers has 
been taken as 1100° F., and we may assume that it is cooled 
in the overhead tube to 100° F., an extent of cooling very 
easily attained. The calculated specific gravity, referred 
to hydrogen, of the gas of which I have quoted the analysis 
being 13-4, we obtain the following data : 

Weight of gas per cubic foot at 1100° F. = -022 lb. 

100° F. = 061 „ 
Weight of atmosphere per cubic foot at 60° F. = -076 „ 

and from these we have on the one hand the increase of 
pressure per foot of height in a flue rising directly from the 
gas producer = -076 - -022 = -054 lb. per square foot, and on 
the other hand the excess of pressure at the foot of the down- 
take from the cooling-tube, over that at the same level in the 
flue, leading up from the gas producer (per each foot of 
height of the cooling-tube) = -061 - -022 = -039 lb. per square 
foot. The height of the cooling-tube above the level of the 
flue that will be sufficient to produce the required pres- 
sure equal to 10 feet of heated gas column, is therefore 

— — x 10 feet - 13 feet 10 inches, or say 14 feet." * 
•039 J 

Siemens further points out that objection has been taken 

1 Siemens, Collected Works, vol. i. p. 222, 



GASEOUS FUEL 



147 



to the use of cooling-tubes on the ground of the loss of heat 
entailed, but he contends that this objection does not hold, 
because there is no advantage in supplying the gas hot to 
the regenerators, and further, that cooling condenses a large 
quantity of moisture which would otherwise be carried into 
the furnace. 

Improvements on the Siemens Producer. — The 
Siemens may be taken as the type from which all modern 
producers have been derived. The development in the more 
recent producers has been mainly in the direction of greater 
economy of heat and 
greater speed of work- 
ing. To attain these 
objects more steam is 
used, and the producers 
are worked closed, so 
that a blast pressure 
can be used instead of 
allowing the air supply 
to depend entirely on 
chimney draught. 

One difficulty with 
the ordinary form of 
producer as described 
was the collection of a 
large amount of tar in 

., -,. , , i_« i FIG. 27. — Siemens Producer arranged for the Destruc- 

theCOOlmg-tubeS, Which tion of Tar . A> Desce nding wall. C, Gas main. 

not only tended to block B > cleanin g door - 

the tubes, but also leaked out and kept the place in a mess. 
To prevent this, and to convert the tar into carbon which 
can be consumed in the producer, and permanent gases 
which will pass away, it is only necessary to heat the tarry 
vapours to a high temperature. This is best done by com- 
pelling them to pass through incandescent coke. This was 
first done in the Wilson producer, but can equally well be 
arranged in almost any type. Fig. 27 shows a Siemens 
producer arranged for the destruction of tarry matters. 




148 



FUEL 



Siemens Circular Producer. — This is a solid-bottom 
open producer. The body consists of a circular shell of brick- 
work cased in iron, and carried on an inverted portion of a 
cone, the smaller end of which rests on a series of short 
columns, from between which the ashes and clinker can be 
withdrawn. The coal is charged by a hopper at the top, 
and the products of distillation are made to descend through 
the incandescent coke on their way to the gas-flue. Round 
the top of the producer runs a flat metal pipe through which 

air passes, and is thus 




heated by the hot 
being then carried down 
by a pipe and into the 
centre of the mass by 
means of a steam jet. It 
will be seen that in this 
producer part of the air 
is supplied by a steam jet 
into the mass of burning 
fuel, and part finds its 
way in by natural draught 
round the bottom. It was 
found, however, very 
difficult to work a pro- 
ducer by means of a 
steam jet and at the 
same time use an open bottom, and this form of producer has 
never come largely into use. 
Closed-bottom Producers. 

Siemens Type. — It is quite easy to modify the Siemens 
type of producer so as to work with a closed hearth and a 
steam jet, all that is necessary being to close up the hearth 
and introduce the steam below the bars. An arrangement for 
doing this was described by Siemens, and it consisted simply 
in closing the ash-pit by air-tight doors and introducing a jet 
of steam. This form of producer has been used to some 
extent, but has not been very successful, the grate area 



Fig. 28. — Siemens Gas Producer, circular form. 



GASEOUS FUEL 



149 



being too small, and the layer of fuel too thin to allow of the 
rapid combustion usually associated with closed-hearth pro- 
ducers. In another form used in some steel works the 
sloping wall is done away with, and the bars are placed 
horizontally so as to give a large grate area. The ash-pit 
is divided into two by a transverse wall, through which passes 
a steam-pipe, from which the steam and air are discharged 
on both sides under the 
bars. 

The Steam Jet.— In all 
closed - bottom producers 
the air must be supplied 
under slight pressure, and 
as a supply of steam is also 
necessary, a steam jet may 
be used to supply both. 
The steam jet seems to 
have been first suggested 
for this purpose by Sie- 
mens, and he has investi- 
gated the nature of the 
action which takes place. 
The form of steam jet 
suggested by Siemens is 
shown in Fig. 30. 

" A very thin annular 
jet of steam is employed in the form of a hollow cylindrical 
column discharged from the annular orifice between the 
two conical nozzles a b, the steam being supplied by 
the pipe c into the space between the two nozzles. The 
inner nozzle a can be adjusted up and down by the hand- 
screw d, so as to diminish or increase the area of the annular 
orifice between the two nozzles for regulating the quantity of 
steam issuing. The air to be propelled by the steam jet is 
admitted from the pipe e through an exterior annular orifice 
surrounding the steam jet, and also through the centre of the 
hollow jet. The tube g, into which the steam jet issues, is 




Fig. 29. — Siemens Closed-hearth Producer. 



150 



FUEL 



made of a conical shape at the bottom, so as to form with the 
annular nozzle b a rapidly converging annular passage for 
the entrance of the air, and the width of this air passage is 
regulated by adjusting the nozzle b by means of the nut h at 
the bottom. The tube G continues to converge very gradually 
for some distance above the jet orifice, the length of the con- 
vergent portion increas- 
ing with the width of the 
annular orifice, the object 
being to ensure the com- 
plete commingling of the 
steam and air within the 
length of the mixing 
chamber g, beyond which 
the tube gradually in- 
creases in diameter in a 
parabolic curve to the 
upper end. 

" The rationale of this 
arrangement is as follows : 
First, by gradually con- 
tracting the area of the 
air passages on approach- 
ing the jet the velocity 
of motion of the entering 
air is so much accelerated 
that before it is brought 
into contact with the 
steam the difference in the velocity of the two currents, at 
the point where they come together, is much reduced, and 
in consequence the eddies which previously impaired the 
efficiency of the steam jet are to a great extent obviated, and 
a higher useful result is realized. Secondly, by the annular 
form of the steam jet the extent of surface contact between 
the air and steam is greatly increased, and the quantity of 
air delivered is by this means very much augmented in pro- 
portion to the quantity of steam employed ; also, the great 




Fig. 30. — Siemens Steam Jet. 



GASEOUS FUEL 



151 



extent of surface tends to diminish eddies. Thirdly, by dis- 
charging the combined current of steam and air through the 
expanding parabolic delivery funnel of considerable length, 
in which its velocity is gradually reduced and its momentum 
accordingly utilized by being converted into pressure, the 
degree of exhaustion or compression produced by the steam 
jet is very materially increased under otherwise similar 
circumstances. The results of a long series of experiments 
with this form of steam jet, both for exhausting and com- 
pressing air, have led to the following conclusions : First, 
that the quantity of air de- 
livered per minute by a steam 
jet depends upon the extent 
of surface contact between 
the air and the steam irre- 
spective of the steam pressure, 
up to the limit of exhaustion 
or compression that the jet is 
capable of producing. Second, 
that the maximum degree of 
vacuum or pressure attainable 
increases in direct proportion 
to the steam pressure em- 
ployed, Other Circumstances FlQ - 31.— The Thwaite Annular Steam Jet. 
. . . ., „,. . , . , , .. Details of head and adjustable nozzle. 

bemg similar, lhird, that the 

quantity of air delivered per minute, within the limits of 
effective action of the apparatus, is in inverse relation 
to the amount of air acted upon ; and that a better result 
is therefore realized in exhausting air than in compress- 
ing it. Fourth, that the limits of air pressure attainable 
with a given pressure of steam are the same in compressing 
and exhausting within the limit of a perfect vacuum in the 
latter case." x 

Thwaite Steam Jet. — This is a somewhat simpler form 
of jet, now largely used. As will be seen, the area of the 
annular steam jet can be easily reduced or enlarged by 

1 Siemens, Collected Works, vol. i. p. 142. 




152 



FUEL 



lowering or raising the inner tube by means of the 
regulating screw. 

The Thwaite Simplex Producer. — This consists of a 
circular iron shell lined with fire-brick, with a grate at the 
bottom, the bars of which are placed slightly sloping ; steam 
and air are blown into the ash-pit. The gas is drawn off at 
the side beneath a curtain wall. The air before being 




FlQ. 32. — Thwaite Simplex Producer. 

used is heated by circulating in a jacket surrounding the 
casing. 

The Dowson Producer. — This producer is also a circular 
iron shell, lined with fire-brick, and provided with fire-bars 
and a closed ash-pit, into which steam and air are blown. 

This producer is usually provided with an apparatus for 
raising the steam required, which consists of a coil of pipe 
heated by the combustion of some of the gas, one end of the 
coil being connected with a water supply and the other end 



GASEOUS FUEL 



153 



with an injector. Coal may be used as fuel, but as this pro- 
ducer is chiefly used for making gas for gas-engines and 
similar purposes, coke is almost always preferred. 

Solid-bottom Producers. — In this type of producer 
there are no fire-bars, but the fuel being gasified rests on the 
solid bottom of the producer, the air and steam being supplied 
at some distance above the bottom. They may be divided 
into two groups : those in 
which the bottom is kept 
dry, and those in which it 
is supplied with water ; 
and the first group may 
be again subdivided into 
those in which the height 
is small relatively to the 
diameter, and the ashes 
and clinker are drawn 
solid ; and those in which 
the height being greater, 
the ashes are fused and 
tapped out in the liquid 
condition. 

The Wilson Producer. 
— The producer which was 
patented by Messrs. 
Brooke & Wilson in 1877 
was one of the first, and 
is still one of the best of this 
used. 

The producer is a cylindrical shell of iron lined with fire- 
brick. The upper part of the interior is made conical, and is 
surrounded by a gas passage, into which the products of dis- 
tillation enter by openings some distance from the top, so that 
in traversing the hot coke the tarry matters are completely 
broken up. The fuel is charged by a hopper at the top, and 
the gases are drawn off from the annular gas ring. The 
arrangement for the supply of steam and air is peculiar but 





^F-¥ = &*£ 



STEAM Mio AIR 



FIG. 33. — Dowson Producer. 

and is very largely 



type, 



154 



FUEL 



very efficient. Across the bottom of the producer is a hollow 
ridge of brickwork, which communicates with the interior of 
the producer by a series of openings on each side. The 
mixture of steam and air is blown into the interior of this, 
and escapes into the fuel by the openings. As the steam and 
air are thus blown into the middle of the producer, the 
diameter must not be so great that the air cannot reach the 
circumference. The usual diameter is about 8 feet but they 

can be made up to 
12 feet. 

The ridge from 
which the mixed air 
and steam are sup- 
plied divides the 
bottom of the pro- 
ducer into two 
halves, each of which 
is provided with a 
cleaning door. When 
it is required to clean 
out the ashes — about 
once each 12 hours — 
the steam supply is 
turned off, and iron bars are put in through small side 
doors, so that the ends rest on the brick ridge, the clean- 
ing doors are opened and the ashes are raked out ; the doors 
are then closed, the bars removed, so that the fuel settles 
down and the steam is turned on — the whole operation only 
occupying a very short time. The fuel consumed is about 
26 lb. per square foot of bottom in ordinary cases, but 
with a good steam supply it may be brought up to 40 lb. 

In some producers, wrongly called Wilson, the conical 
upper portion of the interior is abolished, so that the tarry 
matters are not destroyed. The air is supplied through an 
iron channel connected with an underground air chamber, 
and a strong iron bar is fixed across the producer to carry the 
ends of the cleaning bars. 




Fig. 34.— Wilson Producer. 



GASEOUS FUEL 



155 



The Wilson Automatic Producer. — This is a modifica- 
tion of the ordinary Wilson type, designed by Mr. Wilson to 




Fig. 35.— Modified Type — Wilson Producer. 

avoid the necessity for the periodical stops for cleaning. The 
producer is much of the same form, but is somewhat taller, 

and the air and steam are 
delivered at a much higher 
level. The two halves of 
the bottom are made conical 
instead of flat, and in each of 
these works an Archimedean 
screw, by which the ashes 
are continuously carried 
outwards and discharged. 
The bottom is filled with 
water, which keeps the 
screw cool and at the same 
time acts as a seal to prevent 
the escape of gas. This 
form of producer is said to 

FIG. 36.— Wilson Automatic Gas Producer, be Very Convenient. Though 

of the Wilson type it rather belongs to the water-bottom class. 

The Ingham Producer. — This producer consists of a 

wrought-iron casing lined with fire-brick, the interior being 




156 



FUEL 



made conical. Air is supplied by a flue, over which is a cast- 
iron arch (b) covered with fire-brick. There are also two 
cleaning doors in such a position that they do not get very 
hot and are therefore not likely to warp. 

One producer, 7 feet in diameter and 8 feet 6 inches high, 

gasifies 4 cwt. of 
coal per hour, pro- 
ducing 30,000 cubic 
feet of gas. 

The Taylor Re- 
volving - bottom 
Producer. — This is 
a modern American 
form of producer, 
which has given 
excellent results in 
practice. As in 
most other solid- 
bottom producers 
the shell is cylin- 
drical, and is of fire- 
brick cased with 
iron. The lower 
portion is made in 
the form of an in- 
verted cone, and in 
the centre is an air- 
pipe by which the 
mixture of steam 
and air is supplied high up into the mass of fuel. The 
fuel is supplied by a hopper, and the gas is drawn off at the 
top in the usual way. The bottom is a flat revolving plate, a 
little larger than the opening at the bottom of the chamber, 
and working in a closed ash-pit. The space between this 
plate and the bottom of the producer chamber is such as to 
allow the ashes to take their natural angle of slope. The level 
of the ashes or clinker is kept about 6 inches above the level 




Fig. 37. — Ingham Producer. 
A, Air and steam delivery-tube. B, Brick curb, c, Blower. 
D, Cleaning doors. E, Gas main. F, Valve to main flue. 
G, Tube for escape of gas when valve P is closed. 
H, Valve. 



GASEOUS FUEL 



157 



of steam and air inlet, or about 3 feet 6 inches above the 
revolving bottom. As the ash accumulates the bottom is 
set in rotation for a time until it is reduced to the proper level, 
this being necessary once every six hours or so. The rota- 
tion " causes a grinding, and closes up any passages that may 
have been formed by the action of the blast " : "a few turns 
of the bottom at frequent 
intervals will keep the fuel- 
bed always in a solid con- 
dition." The clinker is 
removed from the ash-pit 
every twenty -four hours. 

Round the lower part of 
the chamber are a series of 
openings by which bars can 
be introduced to break up 
the clinker if necessary. 

The Thwaite Duplex 
Producer. — This is a solid- 
bottom producer, so designed 
as to ensure the complete 
breaking -up of all tarry 
matters and the conversion 
of all carbon dioxide into 
carbon monoxide. It consists 
of two separate chambers or 
producers united by cross 
pipes at top and bottom, the 
lower one being provided with a valve, and communicating 
with the gas main. Air and steam are introduced at the 
bottom of one chamber, and the gas is drawn off at 
the bottom of the other. Suppose* the producer to be at 
work, a charge of coal is let down into, say,' the left-hand 
chamber, and the steam and air are blown into the bottom of 
the same chamber. The products of distillation pass into the 
second chamber, down through the hot coke which it contains, 
aj}d away to the gas main. When the coal is completely 




Fig. 38. — The Taylor Revolving-bottom Gas 
Producer. 9 feet inside diameter. 



158 



FUEL 



carbonized, a charge is let down into the right-hand chamber, 
and the valves are reversed. The direction of the current is 




±'IG. 39. — Thwaite Duplex Producer. 

usually reversed every ten minutes, either automatically or 
by hand. The gas is quite free from tar and is therefore well 
suited for use in gas-engines. 

Blast-furnace Type of Producers. 
— These have not at present been 
largely used. The first, Bischof 's, was 
almost of this type, though it was 
provided with fire-bars and the clinker 
was not fused. That of Ebelmann, 
which was the next one invented, was 
much more blast-furnace-like in type. 
It resembled a small blast-furnace, 
about 10 feet high and 3 feet 4 inches 



^w^TwmTw^S ii m - diameter at its widest part, the air 



fig. 40.— Ebeimann's Ga 8 being forced in through twyers in the 
Producer. usual way. The clinker was fused 

and tapped out, iron slag being added to increase its 
fusibility. 




GASEOUS FUEL 



159 



Water-bottom Producers. — In this type of producer 
the ashes or clinker are received in a vessel of water, so 
arranged as to act as a seal and thus prevent the escape of 
gas. 

The Dawson Producer. — This producer, designed by 
Mr. Bernard Dawson, was one of the first of its type. " In 
this producer advantage is taken of an old idea in the shape 
of a water bottom. A water trough forms the base of the 
whole structure, and into this the ash and clinkers fall, the 
water forming at the same time a seal which prevents the 
blast escaping. The ash is raked out by hand from time to 




Fig. 41. — Dawson Gas Producer. 

time, and no arduous labour is required to get away the 
clinkers. The steam from the water trough probably assists 
in breaking up the clinker, as it falls into the trough by 
natural gravitation. The producer itself is very similar to 
the ' Wilson ' in external appearance, but the fuel rests on a 
cast-iron hopper — an inverted cone — in the centre of which 
is an opening for the passage of the ash downwards and the 
blast upwards. Below this hopper is an open space showing 
connection with the injector, and kept tight by means of 
saddles dipping into the water trough. The top of the pro- 
ducer is dome-shaped, and all the internal structure is so 
arranged that no special blocks are required in the building. 
A man-hole is placed at any convenient part, the only door 



160 



FUEL 



in the apparatus, and is used only when repairs are going on 
inside. This is a great advantage of itself over the old system, 
where doors had to be opened, screwed up, and luted tight. 
Producers of this kind have worked for months at a time 
without being stopped at all — a near approach to the case of 
the blast-furnace." * In a more modern form the cast-iron 
hopper is dispensed with, and its ashes rest on the bottom of 
the water trough. 

The Duff Producer. — This is one of the most popular 
producers in use. The casing is circular, but the lining is 





Fig. 42. — Duff Producer. From Engineering. 

so arranged that the fuel chamber is rectangular, the casing 
dips down into the water trough so as to form a water seal, 
and across the chamber pass three bars, on which rest two 
sets of inclined fire-bars forming two inclined grates. The 
steam and air are blown in beneath the grates and pass up 
through the fuel, whilst the ashes and clinker slip off the 
grates into the water and are easily removed, the fall being 
aided when necessary by poking with iron rods introduced 
through holes left for the purpose in the casing. 

The Thwaite Small-power Gas Generator. — In this 
generator the fire-grate is formed of a girdle of suspended 



1 Gas Producers, by R. Booth, M.I.M.E. Read before the Civil and 
Mechanical Engineers' Society, 17th February 1893, 



GASEOUS FUEL 



161 



fire-bars that hang from a truncated cone casting, supported 
from the outside casing. The fuel at the base thus takes a 
cone-shaped form. The ashes descend into water, and the 
heat of the clinkers evaporates part of the water, the vapour 
ascending through the fuel, adding hydrogen to the gas 
produced. 





n 












n — * 
















' <Vr''' r "\ 






!v,S *y\ ,,;'' j 










1 


A 5 '-- -'-I 




^^ , -— J 


Af 'V >>*■'''- 7/ 




^^^j^— 


yfeg 


■ • -n: 





Fig. 43.— Thwaite Small-power Producer. 

The clinker and incombustible matter can easily be 
removed, without arresting the progress of gas-making, by 
inserting a rake or bar below the surface of the water, and 
below the seal formed by the side plates of the gas generator. 
In this " hanging " form of grate, the ash does not reduce 
the grate efficiency, as it does not offer a suitable surface 
for the repose of either coke or clinker. It is self-cleaning, 
and there is little chance of the air supply being hindered. 



( D 107 ) 



M 



162 



FUEL 



As shown by the direction of the arrows, the air-blast 
supply passes round the air belt encircling the gas generator, 
and is consequently heated by contact with the heated plates. 

The Smith and Wincott Producer. — Central blowing 
is in general the most satisfactory, but one of the difficulties 
with most centre-blown producers is that of keeping the 
blower clear of clinker. This has been overcome very satis- 
factorily in this producer. The producer is circular, about 
8 feet in diameter inside. The air main enters the bottom of 
the producer, and then spreads out into the form of an in- 
verted cone about 2 feet 6 inches in diameter and 2 feet high, 




Fig. 44. — The Smith and Wincott Producer. 

the periphery of which is perforated with a large number of 
slits, the main being covered with an iron cap. The air slits 
sloping inward instead of outwards cannot be blocked by 
clinker, and the large circumference of the cone ensures a good 
distribution of air and complete combustion. The shell dips 
down into a water trough forming a water seal as usual. 

The Mond Producer. — In connection with the pro- 
duction of Mond gas (see p. 177) Dr. Mond designed a pro- 
ducer which has some special features. The producer is 
circular and is tapered towards the bottom, the grate is a 
hanging grate made up of an inverted cone of fire-bars the 
ends of which are well above the level of the water in the 



GASEOUS FUEL 



163 



water trough. The producer has a double shell. The inner 
shell is lined with fire-brick, as usual, and the outer shell is 
placed so as to leave a space between it and the inner shell 
through which the air and steam on its way to the producer 
can pass and thus become heated. The outer shell is carried 
downwards so as to dip into the water in the trough and 







Fig. 44a. — Mond Producer for Non-recovery Plant. 

form a seal. The fuel is supplied by a long charging hopper 
round which the gas circulates so as to heat and partially 
distil the coal before it sinks into the body of the producer. 
The type of producer now usually supplied for the 
manufacture of Mond gas is illustrated in Fig. 44a. Under 
conditions of ammonia recovery the only difference in the 
producer is the addition of a central bell through which 
the fuel is charged. 



164 FUEL 

Kerpely Producer. — One of the most successful pro- 




ng. 45. — Sectional Diagram of Kerpely Producer. 

ducers using mechanical grates i§ the Kerpely illustrated 



GASEOUS FUEL 165 

in Fig. 45. This is able to deal with coal containing 40 per 
cent of ash. The chief features are the eccentric rotating 
hearth which automatically discharges the ash at one side, 
and the mechanical rotating pokers which prevent the forma- 
tion of blow-holes in the fuel bed. In other designs the 
producer is jacketed with an annular boiler for the produc- 
tion of low-pressure steam and consequent greater fuel 
efficiency. 

Gas for Gas-engines. — When the gas is to be used for 
gas-engines it must be cleaned by being passed through 
scrubbers or washers to remove the tar and dust. As the 
gas production with pressure producer is continuous, a gas 
holder must be provided to hold the excess gas. The holder 
also serves a useful purpose in governing the gas pressure. 



SUCTION PRODUCEBS 

When the gas is required only for working gas-engines, the 
quantity required is usually not very large, and it is incon- 
venient to provide gas holders to hold the gas, and it is also 
often inconvenient to provide separate boilers for raising 
steam. To overcome these difficulties suction producers have 
been designed. In these the air and steam mixture is drawn 
into the producer by the suction of the engine, so that gas 
is only made as it is required, and steam is raised by the 
waste heat of the gases. A large number of these suction 
producers are now on the market, but it will be sufficient to 
describe two or three as types. 

The Dowson Producer. — This is a circular producer of 
the bar-bottom type. The fuel is supplied by means of a 
cylindrical hopper, and round the top of the producer, de- 
scending nearly as low as the bottom of the hopper, is the 
steam generator, or evaporator, which is in the form of a 
ring. The hot gases, passing through the space between the 
coal hopper and the evaporator, heat them both before pass- 
ing away. The water is supplied from a feeder to a ring 
which runs round inside the evaporator, and there it is 



166 



FUEL 



allowed to drop into the boiler and is at once converted into 
steam. The air enters the steam generator, circulates round 
it, and passes with the steam to the space beneath the fire- 
bars. 




*mm?s. 



FIG. 45A. — Dowson Suction Producer Plant. 

The Campbell Generator. — This generator differs from 
that of Mr. Dowson mainly in the way in which the steam is 
raised and supplied. The steam is produced from a boiler 
placed at the top of the producer, and therefore heated by the 
gas as it passes away. The air is drawn into the boiler above 



GASEOUS FUEL 



167 



the water, and thus becoming laden with steam, passes by a 
pipe to the space beneath the fire-bars, and hot gas is made 
to circulate round the pipe so that the air and steam become 
superheated. 

The Watt Producer. — This is a cylindrical bar-bottom 
producer, but differs from those described above in the way 
the steam is produced and in some other respects. A space 
of about 1| inches wide is left round the body of the producer 
for the passage of the gas to the scrubber, and outside this 



CQ. 





— £ 



Us 



S 



*SJL',s 



T—T 



FiQ. 46. — Campbell Gas Producer and Cleaning Plant. 

is another casing so arranged as to leave a second annular 
space the same width as the first, and the whole is enclosed 
in a non-conducting casing. The top of the producer is 
covered with a cone of corrugated iron plate, the corrugations 
being arranged so as to form a continuous spiral trough. 
On the outside of the intermediate iron casing a spiral trough 
continuous with that on the cover is fixed. The whole is 
covered with an iron cover. The water is supplied near the 
centre of the conical cover and flows round, being vaporized 
as it goes, and any that remains flows down the trough in the 
casing, where it is completely vaporized. Air is admitted to 



168 FUEL 

the space above the corrugated cover, and, passing down the 
outer annular space, carries the steam with it to the space 
beneath the fire-bars. The fire-bars are arranged so that 
they can each be turned separately and drawn if required. 

Starting. — With any of these producers, and indeed with 
all producers of the suction type, some provision must be 
made for starting, for the gas is to drive the engine, and no 
gas can be made until the engine is started and thus draws 
the air through. To start, a small fan, worked by hand, is 
usually attached to the converter, and this is worked until 
the producer is hot enough to begin gas-making, the pro- 
ducts of combustion during this time being allowed to burn 
to waste at an escape pipe. With the Watt producer the 
fan is sometimes dispensed with, a natural draught being 
produced first by heating the waste pipe by means of a small 
fire, and then by combustion of the waste gas at the waste 
pipe. 

Cleaning the Gas. — For gas for gas-engines, charcoal, 
coke, or anthracite is always used, as if bituminous coal is 
used it is extremely difficult to remove the last traces of tar. 
Even blast-furnace gas, purified as described in Chapter 
VIII., is not free enough from tar for use, but has to be 
subject to a further purification. This is usually done by 
passing the gas through a series of small apertures and allow- 
ing it to impinge on a flat surface, by which the last traces of 
tar are removed. The gas made from charcoal, coke, or 
anthracite also needs purification, but this is much more 
easily effected, the impurities to be removed being almost 
entirely dust, carried over mechanically, and traces of tar 
from bituminous matter left in the coke, and a quantity of 
water either from moisture in the fuel or from undecomposed 
steam passing through the producer. To remove these the 
gas is passed through a scrubber filled with some suitable 
material down which a rain of water is kept falling, thus at 
the same time cooling and cleaning the gas. The scrubber 
consists of an iron cylinder 10 feet or more in height and 2 
or 3 feet in diameter, or more according to the quantity of 



GASEOUS FUEL 169 

gas passing through, the capacity being about 1-25 times the 
amount of gas produced per minute, though even larger 
scrubbers may be used with advantage. A grate is usually 
fixed across the bottom of the scrubber, and the space above 
this is filled with some distributing material. Coke broken 
up into small pieces is often used, and works very well as a 
dust-catcher. Water is distributed by means of an arrange- 
ment of pipes over the top of the coke, and running down 
meets the ascending current of gas. The amount of water 
required will be about 1 gallon per hour for each 50 to 75 
cubic feet of gas made per hour, but it will vary with the 
temperature of the gas and other conditions. 

To avoid the gas lighting back, the gas, before passing 
into the scrubber, is always passed through a vessel of water, 
which forms a water seal, the details of the arrangement 
varying with the different types of plant. 

When there is a small quantity of tar, a saw-dust scrubber 
is often used. This consists of a rectangular chamber with 
the inlet on one side and the outlet on the other, and across 
this are fixed two perforated plates, the space between which 
is filled with coarse saw-dust which is kept moist, and through 
which the gas has to pass. If the quantity of tar is large, 
the gas before entering the scrubber is often passed through 
a tar extractor, which is usually a closed vessel fitted with 
a large number of plates against which the gas is directed as 
it flows. The actual arrangement of the scrubbing plant 
varies very much, each maker having his own design. The 
illustration (Fig. 46) shows the arrangement in the Campbell 
plant. 

Cost of Working, &c. — Suction-gas plants are mostly 
used for making gas for driving small gas-engines which 
otherwise would be driven by coal-gas derived from the town 
supply. Which will be the cheaper will depend on various 
circumstances, but largely, of course, on the price at which 
coal-gas can be obtained. The cost for fuel in running a 
suction-gas plant is comparatively small, and may be taken 
in the case of a good plant as being about 0-3d. per B.H.P. 



170 FUEL 

hour, provided suitable anthracite or coke can be obtained at 
a low price, say 35s. or so a ton. In addition to this there 
will of course be the depreciation of the plant, the interest on 
the cost of plant, the labour at the plant, and other items, 
which run the actual cost up very considerably, so that the 
actual cost can only be obtained by a careful consideration 
of each case on its own merits. As the ratio of the calorific 
powers of town gas and suction-gas is about 4t\ : 1, it follows 
that the cost of the latter per 1000 cubic feet must be 
reduced to a fifth of that of the former to make the installa- 
tion of suction-gas a commercial proposition. It must of 
course be remembered that the fuels necessary for suction 
producers — anthracite or coke — are much more costly than 
the dross which can be used for large installations of pressure 
producers. 

Use of Steam in Gas Producers. — The use of steam as 
a means of enriching producer-gas has already been briefly 
mentioned, and, as will be seen from the descriptions of the 
different forms of producer, its use is now universal. 

The reaction C +0, by which the gas is obtained, is exo- 
thermic, and is accompanied by the evolution of a large 
quantity of heat. 

The heat value of the reaction C +0 = CO is 29,300 +C. 
units, or 52,700 B.Th.U., whilst the heat value of the reaction 
C +20 =C0 2 is 97,300 C. units, or 175,100 B.Th.U., so that 
about one-third of the heat which the coke could evolve by 
combustion is given out in the producer, and is therefore lost 
for practical purposes. It is usually stated that about one- 
third of the available heat of the fuel is used in converting the 
coke into gas, but this statement is not correct ; it should be, 
that one-third of the available heat is evolved in converting 
the coke into gas, which is quite a different matter. 

In the case of the conversion of water into steam there is 
an absorption of heat in doing work, and this can only be 
recovered when the work is undone, i.e. when the steam is 
converted back into water ; but in the case of the formation 
of carbon monoxide from carbon and air, heat is evolved, 



GASEOUS FUEL 171 

only it is evolved in the wrong place — in the producer, where 
it is not required, instead of in the furnace, where it is. The 
action of the steam is to utilize some of this heat and transfer 
it to the furnace, so that though the actual calorific power of 
the fuel is not altered, its available heating power is much 
increased. 

When steam is blown over hot charcoal or coke it is de- 
composed thus, H 2 + C = CO + 2H, so that each pound of 
carbon gives the same amount of carbon monoxide that it 
would have done had it been burnt with oxygen, and in 
addition an equal volume of hydrogen. This reaction is 
endothermic, that is, it absorbs a large quantity of heat. It 
may be regarded as made up of two reactions, and the actual 
thermal value will be the algebraic sum of these. 

The decomposition of water absorbs heat, the amount of 
heat absorbed being the same as that evolved in the forma- 
tion of the water. The heat value of the reaction 2H + O = 
H 2 is 123,100 +B.Th.U., so that the value of the decom- 
position will be 123,100 -B.Th.U. 

.-. Decomposition of water . . . 123100- 

Formation of carbon monoxide . . . 52700 + 



Heat of the double reaction . . . 70400 

Every pound of carbon, therefore, which is burnt by means 
of steam absorbs 5880 British units of heat. 

It is quite obvious, therefore, that the quantity of steam 
which can be used is limited, for unless enough heat be 
supplied in some other way to make up for this absorption of 
heat, and also to make up for all losses in the producer, the 
temperature will fall and the action will cease altogether. 

Assuming that there were absolutely no loss of heat, and 
that the temperature were high enough to start the reaction, 
about 1-4 lb. of carbon must be burnt by air to supply the 
heat necessary for the combustion of 1 lb. of carbon by 
steam. 

In this case the heat evolved by the combustion of the gas 
would be identically the same as that which would be evolved 



172 FUEL 

by the combustion of the solid carbon. This may be seen 
from the following figures : 



. 122400 + 
2H+0 = . . . 123100 + 



70400 



245500 + 



Difference 174900 + 

There is therefore no loss of heat. The steam only effects 
the transference of some of the heat from the producer to 
the furnace. 

It need hardly be said that these conditions can never be 
even approached in practice, and that therefore the quantity 
of steam used is always very much less than the maximum 
shown above. 

The proportions of steam and air used are usually given 
by volume. In round numbers, 1 volume of steam contains 
as much oxygen, and is therefore as efficient for burning 
carbon, as 5 volumes of air. For combustion of carbon in 
the theoretical ratio 1 part by steam to 1*4 parts by air 
would require the steam and air to be in the ratio of about 
1 : 7, or the mixture would contain about 12-5 per cent steam 
and 77-5 per cent air. The maximum proportion of steam 
used in practice in ordinary producers is about one-third of 
this, or perhaps in rare cases a little more. The amount of 
steam used does not depend entirely on the amount supplied, 
since, if it be used in excess, some may escape undecomposed. 

Calculation of Composition of Gas. — Assuming that 
coke or charcoal is the fuel fed into the producer, and know- 
ing the composition of the mixture of air and steam supplied, 
it is possible to calculate the composition of the gas, and also 
the amount of heat lost in its preparation. Assume that the 
mixture of air and steam supplied contains 5 per cent of steam 
and 95 per cent of air — i.e. in 100 litres, 5 litres of steam and 95 
litres of air — 5 litres of steam will contain oxygen which in 
the free condition would occupy 2-5 litres, and the 95 litres of 
air will contain (assuming 21 per cent of oxygen) 19-95 litres of 



GASEOUS FUEL 173 

oxygen, and of course 75-05 litres of nitrogen. Since water 
vapour contains its own volume of hydrogen which will be 
liberated, the resulting gas will contain 5 litres of hydrogen. 
Since oxygen gives twice its own volume of carbon monoxide, 
the composition of the gas will be — 



Hydrogen .... 


5 litres 


= 4-00 per cent 


Carbon monoxide from steam . 


• 5 


= 4-00 


Carbon monoxide from air 


. 39-9 „ 


= 31-90 


Nitrogen .... 


. 7505 „ 


= 6010 




124-95 litres 


= 100-00 



It is possible to calculate also the amount of heat saved by 
the use of the steam ; the amount of carbon burnt by steam 
compared with that burnt by air is in this case as nearly as 
possible 1:8; so that 

1 lb. of carbon burnt by steam . = 5870 - B.Th.U. 

8 lb. of carbon burnt by oxygen =4390 x8 , . =35120 + 



Heat evolved in producer . . . . . = 29250 + 

Or for 1 lb. of carbon = 3250 + 

Total heat which could be evolved by the combustion of 

1 lb. of carbon to carbon dioxide . . . = 14600 4- 

Loss per cent = 22 as against 33 when no steam was used. 

In the calculations, it has been assumed for simplicity that 
coke is the fuel used. In practice coal is nearly always used 
for central producers. This is coked at the top of the pro- 
ducer, the products of distillation mixing with the gas which 
rises from below, so that the gas actually obtained is a 
mixture of the gas produced by the action of air and steam 
on the coke with that resulting from the distillation of the 
coal. The gas is, therefore, richer in hydrogen and hydro- 
carbons, and has a higher calorific power than that which 
would be obtained from coke. 

Sources of Loss of Heat in Gas Producers. — There 
are many sources of loss of heat in the gas producer, and the 
aggregate of them determines the maximum amount of steam 
which can be used, since all losses must be made up by the 
combustion of the coke by air. Some of these sources of 
heat are peculiar to the producer, and therefore militate 



174 FUEL 

against the efficiency of gaseous fuel ; others are common to 
all classes of fuel. The sources of loss are — 

1. Heat carried away by gases. 

2. Heat lost by radiation. 

3. Heat absorbed by dissociation of the solid fuel. 

4. Heat carried out with clinker, etc. 

5. Carbon dioxide in the gases. 

6. Water in the gases. 

1. Heat carried away in Gases. — This is a very large item 
in all ordinary forms of producer, as the gases escape at 
a very high temperature. In the open-hearth types of pro- 
ducer it is necessary to allow the gases to escape hot, in order 
to produce a draught, but with the closed-hearth producers 
there is no need for this, and the cooler the gases are the 
better, as there seems to be no advantage in sending the gas 
hot to the regenerators. 

Taking for simplicity a producer fed with coke ; for each 
pound of carbon consumed there will be about 6-8 lb. of gas, 
and assuming this to escape at a temperature of 600° F. the 
amount of heat carried away by it will be 6-8 x 600 x -25 = 
1070 units, or about \ of the heat evolved in the producer 
when 5 per cent by volume of steam is used. If the tempera- 
ture were 1000°, 1700 units of heat would be thus lost. 

2. Heat lost by Radiation. — This is probably very consider- 
able in all cases, but no sound estimate can be made as to its 
amount. In some forms of producer it is utilized in heating 
the air. 

3. Heat due to Dissociation. — Undoubtedly, the dissocia- 
tion of the coal into coke and gaseous products absorbs some 
heat ; the amount is, however, probably small and has not 
been determined. It is of little practical importance, as the 
same loss takes place when solid fuel is burnt in an ordinary 
fire. 

4. Heat carried away in Solid Products. — The heat due to 
the high temperature of the solid products is of little moment, 
as it is usually small in amount. In water-bottom producers 
there is little loss from this source, as any heat is utilized in 



GASEOUS FUEL 175 

volatilizing some of the water. In bar-bottom producers 
there is often considerable loss from unburnt carbon falling 
through the bars. 

5. Carbon Dioxide in the Gases. — Most producer-gas con- 
tains some carbon dioxide, and the presence of a considerable 
quantity is not infrequent. This is probably the most 
serious source of loss in most forms of gas producer. The 
presence of carbon dioxide is always due to the column of 
fuel either not being deep enough or not hot enough to de- 
compose all the carbon dioxide which may be formed. When 
it is remembered that the conversion of a pound of carbon 
into carbon dioxide evolves about three times as much heat 
as the conversion into carbon monoxide, it will be seen that 
a very large amount of heat may thus be lost, and the 
efficiency of the gas very seriously diminished. No producer 
can be considered as being satisfactory which allows a very 
large quantity of carbon dioxide to pass into the gas. 

6. Excess of Steam. — This is also very objectionable, and is 
due to the supply of more steam than the coke can decompose 
under the conditions of working. Steam has a high specific 
heat and a high latent heat, so that it may carry away a 
considerable quantity of heat. 

The actual loss from all sources has been variously 
estimated. It should not exceed 15 to 20 per cent of the 
available heat of the fuel, but it is often very much more. 
Siemens gives 12 per cent, but this is certainly too low. 

Working the Producer. — With the introduction of the 
closed-hearth producers the need for a draught, and therefore 
for the overhead cooling-tubes, disappeared, and in all modern 
plants they have been dispensed with, underground flues being 
substituted. It is still a moot point whether any advantage 
is to be gained by sending the gas to the regenerators hot, but 
no attempt is made now to cool the gases, and where the old 
overhead flues are still used, they are very frequently thickly 
lined with fire-brick so as to prevent cooling. Unless the tar 
be destroyed by passing the gas through hot fuel — as is done 
in many of the producers already described — the gases on 



176 FUEL 

cooling will deposit tar and sooty matters, which are trouble- 
some. If, however, the gases be kept hot there is compara- 
tively little deposition, most of the tarry materials being 
carried over to the furnace and burned. In some cases an 
excess of steam is intentionally used, it being contended that 
the steam coming in contact with the tarry matters in the 
regenerators will convert them into carbon monoxide and 
hydrogen, which are thus added to the gas. 

The cleaning of the flues is often a matter of considerable 
trouble, and in most cases the tarry matters are burned out. 

MOND GAS 

M. Mond obtains a gas very different from ordinary pro- 
ducer-gas by using a very large excess of steam. The pro- 
ducer used is of the water-bottom type, and is described on 
p. 162, but any other type will do, and the Duff producer 
is often used. About 2| tons of steam is blown in for each 
ton of coal consumed, the greater portion of it passing through 
undecomposed. Each ton of coal yields about 130,000 cubic 
feet of gas, which has the composition on an average : 





By Volume. 


By Weight 


Carbon dioxide 


. 17-1 


320 


Carbon monoxide . 


110 


131 


Olefines . 


•4 


•5 


Marsh -gas 


1-8 


1-2 


Hydrogen 


27-2 


2-2 


Nitrogen 


42-5 


510 



1000 1000 

Combustible gas, per cent . 40-4 17-0 

The amount of heat lost in the producer is said to be not 
more than about 25 per cent of that obtainable from the coal, 
so that it will be seen that the gas, though very different from 
ordinary producer-gas, has about the same heating power, 
and is made with about the same loss of heat. 

If the steam be decomposed by carbon, so as to produce 
carbon monoxide, 1 lb. of carbon would require 1J lb. of 
steam. As, however, a considerable portion of the carbon 



GASEOUS FUEL 



177 



must be burnt by air, it may be said roughly that only about 
1 ton of steam can be used for each ton of carbon consumed, 
so that lj tons must pass through undecomposed, and this 
must be condensed. The plant is arranged by Dr. Mond so 




Fig. 47. — Section of Mond Producer. 

as to condense this steam and recover as much as possible 
of the heat. 

The gas first passes through a set of " regenerators.' ' 
These are double, vertical iron tubes. The hot gas passes up 
the inner tube, and the air and steam on its way to the pro- 

(D107) w 



178 FUEL 

ducer passes down through the annular space between the 
two tubes. From the regenerator the gas passes to a washer, 
a horizontal vessel containing water, and fitted with mech- 
anical dashers by which a large quantity of spray is thrown 
up, through which the gas has to pass. The gas is thus 
cooled to about 90° C, and a considerable quantity of water 
is condensed. From the washer the gas passes to the acid 
tower, a tall tower filled with a chequer-work of acid-brick 
down which a rain of sulphuric acid is kept falling, the 
ammonia being thus converted into sulphate and carried 
down in solution. From the top of this tower the gas, still 
hot, but deprived of its ammonia, passes to the gas-cooling 
tower which is packed with wood, or earthenware rings, and 
down which cold water is kept falling. This still further cools 
the gas and heats the water, and the gas is passed on to the 
engines where it is to be used, or to the gas-holders for storage. 
The hot water may be pumped to the top of another tower, 
down which it falls and meets the air which is forced in to 
supply the producer, which thus becomes saturated with 
moisture and is then carried through the regenerators to the 
producer, but the more usual procedure is to cool the circu- 
lating water by an atmospheric cooling tower. 

The ammonia liquor is run into a settler so that any tar 
can separate, a small portion of the liquor is drawn off, and 
fresh acid added so as to keep the liquor distinctly acid, and 
it is then pumped again to the top of the ammonia tower. 
The ammonia liquor and tar are treated exactly as described 
in Chapter VIII. 

The amount of ammonia recovered varies almost in pro- 
portion to the nitrogen content of the coal used, and is usually 
equivalent to about 65 lb. of sulphate per ton of coal for a 
content of one per cent, this representing about 60 per cent 
of the total possible as against 15 per cent in ordinary retort 
carbonization. 

It must be remembered that the nitrogen is not present 
in the coal as ammonia, but in organic compounds which 
are broken up by the distillation of the coal, and which in 



GASEOUS FUEL 



179 



presence of the very large quantity of steam are carried 
off undecomposed in the form of ammonia. 

The first cost of the plant is large, and the cost of raising 
steam may be considerable, but these are usually more than 
balanced by the value of the ammonia recovered. 

The Blast-furnace as a Gas Producer. — The iron- 
smelting blast-furnaces are the largest gas producers in the 
world. The gas is merely a by-product, and though it has 
been used for heating the blast for working the furnaces, 
and for other purposes, it is only recently that much attention 
has been given to it. The gases from blast-furnaces are of two 
kinds, depending on whether coke or coal is used as the fuel. 

If no changes other than those produced by the action of 
the air on the coke took place, the gas would be exactly of the 
nature of producer-gas ; but the furnace is used for smelting, 
and this modifies the result. The air blown in at the twyers 
at once attacks the carbon, forming carbon monoxide, which 
rises up through the charge. Coming in contact with oxide 
of iron it reduces it, at the same time being converted partially 
into carbon dioxide, Fe 2 3 + 3CO = 2Fe + 3C0 2 , which thus 
mixes with the gas, and as this change takes place at a 
temperature below that at which carbon can act on carbon 
dioxide this gas is not decomposed. Limestone is also added 
as part of the charge, and this is split up at high temperature 
into lime and carbon dioxide, CaC0 3 = CaO + C0 2 ; as, how- 
ever, the temperature at which this reaction takes place is 
high, the resulting carbon dioxide is wholly or partially con- 
verted into carbon monoxide. 

The following analyses (by volume) of gas from coke-fed 
blast-furnaces will indicate its nature : 





1. 


2. 


3. 


4. 


Carbon dioxide 
Carbon monoxide . 

Nitrogen 

Hydrogen 

Hydrocarbons .... 


11-39 

28-61 

57-06 

2-74 

•20 


1201 

24-65 

57-22 

519 

•93 


•9 
34-6 
64-4 

1 


5-9 
29-6 
63-4 

11 



1, Coke, Ebelmann. 2, Charcoal, Ebelmann. 3, Coke, Thwaite. 4, Charcoal, Thwaite. 



180 



FUEL 



Owing to the quantity of inert gases present the calorific 
power of the gas is low. Taking No. 1 as a type, the calorific 
power can be calculated. 



Carbon monoxide 

Hydrogen 

Methane 



0-2861 x 320 = 91-6 B.Th.U. 
00274 x 321 = 8-8 
00020 x 998 =* 20 



B.Th.U. per cubic foot 



102-4 



In Scotland, and in some parts of England, the furnaces 
are fed with splint-coal, raw, i.e. uncoked. The gases are 
therefore enriched by the admixture of the products of dis- 
tillation of the coal. 

The following analyses show the nature of these gases : 



Carbon dioxide 
Carbon monoxide 
Hydrogen . 
Marsh-gas . 
Nitrogen . 
Ammonia . 



1. 


2. 


3. 


4. 


8-57 


8-61 


5-4 


6-79 


2715 


2806 


301 


26-40 


5-48 


5-45 


6-2 


12-23 


4-29 


4-37 


3-2 


1-71 


54-29 


53-38 


55- 1 


52-87 


not est. 


•13 




•• 



No. 1 has a calorific value of 147 B.Th.U. per cubic 
foot. 

It will thus be seen that the gases are quite comparable 
with those of a gas producer and are better than some, for 
there are many cases in which producer-gas contains as much 
carbon dioxide as blast-furnace gas (see table of analyses, 
p. 192). In iron-works the gas obtained is usually far more 
than enough to drive all the plant of the works, and in some 
cases has been utilized in addition for steel-making and other 
purposes. 

The blast-furnace is probably the most perfect gas- 
producing plant, and this for several reasons. 

1. Owing to the high column of material the gases can be 
effectively cooled. This cannot be so well done, however, 
owing to the chemical reactions, in a blast-furnace used for 
smelting as it could in one used only for ga§ producing. 



GASEOUS FUEL 181 

2. Owing to the depth of the column of material and its 
high temperature, the gas as it passes up is quite free from 
carbon dioxide, that gas being subsequently added by chemical 
reactions which would not take place in a blast-furnace used 
only for gas-making. 

3. Owing to the slag being tapped out in the liquid 
condition there is no loss by the escape of unconsumed 
carbon. 

Comparison of Gas Producer and Blast-furnace. — 
Gas producers are usually worked at a very low pressure, 
2 to 10 inches of water, and the amount of coal gasified is 
usually about 25 lb. per square foot of grate area or bottom 
per hour, reaching a maximum of 40 or 50 lb. in very quick 
driving. 

A blast-furnace is worked at a much higher pressure, 2 J to 
7 lb. per square inch. An ordinary furnace with a hearth, 
say 8 feet in diameter, will consume, i.e. gasify, about 70 tons 
of coal in the 24 hours, which is equal to about 130 lb. of 
coal per hour per square foot of bottom, and with larger 
furnaces the consumption is very much greater. It is a 
wonder that the blast-furnace type of producer has not been 
more largely used, for it offers advantages that are not 
possessed by any other form. Steam could readily be used, 
and a rate of production reached in excess of that at present 
given by any producer in use, whilst the sources of loss due 
to the escape of hot gas and the production of carbon dioxide 
would be effectually diminished if not stopped. 



WATER-GAS 

When steam is passed over red-hot coke, as already ex- 
plained, a mixture of carbon monoxide and hydrogen is pro- 
duced which is called, very improperly, water-gas. As this 
reaction is powerfully endothermic, heat must be supplied 
either by working the apparatus intermittently, or by heating 
the retort in which the action takes place by separate 
fires. 



182 



FUEL 



Plant at the Leeds Forge. — Most of the water-gas 
plants erected in this country have been on the principle of 
that erected at the Leeds Forge. This consists simply of a 
producer without any regenerative chamber. It is circular 
in form, lined with fire-brick, and provided with a charging 




FIG. 48. — Water-gas Plant at Leeds Forge. 

hopper at the top. The fuel used is usually coke. Air is 
blown in at the bottom, and thus the coke is consumed and 
the temperature rapidly rises, the producer-gas obtained 
either being allowed to burn at the chimney, or being con- 
ducted to steel or other furnaces for use. When the coke is 
sufficiently hot the air and producer-gas valves are closed, 



GASEOUS FUEL 



183 



'TUHPOKDOIMKOlt 
Of HATER 6AS 



and steam is blown in at the top of the producer, the 
water-gas escaping at the bottom and passing to a gas- 
holder. When the coke is sufficiently cool the currents 
are reversed, and air is sent through till it is again hot 
enough to produce water-gas. The times at the Leeds forge 
are about 4 minutes gas -making and 10 minutes heating 
up. The coke yields about 34,000 cubic feet of water-gas 
per ton. 

The Loomis Producer. — This is one of the most recent 
and successful forms of water-gas plant, and is an improve- 
ment of the well-known 

Os 

Lowe system. It consists 
of a cylindrical casing about 
12 feet x 9 feet, lined with 
fire-brick. At the top is a 
charging door, and at the 
bottom a fire-brick grate 
over an ash - pit, across * 
which are placed slabs of 
fire-brick. The ash-pit is 
provided with a door, and 
also a brick-lined tube lead- 
ing to a boiler, and thence 
to an exhauster. The producer is provided with a cleaning 
door, and also with a series of ports leading to the gas main. 
Coal or coke may be used as fuel. The producer being 
charged, the charging door is left open, the exhauster set in 
action, and air is drawn downward through the charge ; the 
producer-gas thus obtained, passing through the ash-pit, heats 
the superheating slabs to a very high temperature, and pass- 
ing to a boiler gives up its sensible heat for steam raising. It 
is then passed to a gas-holder. As soon as the charge is 
sufficiently hot the charging door is closed, steam is blown 
into the ash-pit ; passing over the hot superheating slabs it 
becomes strongly superheated, and then passing up through 
the hot coke, water-gas is formed which is pumped by the 
ports to the water-gas holder. 




^ rococo 



Fig. 49 



Loomis Gas Producer. 
From J. I. and S.I. 



184 



FUEL 



Mr. Loomis gives the following estimate as the cost per 
1,000,000 cubic feet of gas with coal at $3 per ton : x 



Coal, 25 tons at $a.00 

Coal for steam, 3 tons 

Labour 

Supplies and repairs 

Purifying 



$75.00 

9.00 

22.00 

4.00 

5.00 



Received for producer-gas 
Interest and depreciation 



115.00 
40.00 

75.00 
25.00 

100.00 



Or cost per 1000 cubic feet, $0.10 =say 5d., or if the producer- 
gas be lost, $0.14, say 7d. 

The Strong Producer. — In this producer, which is 
largely used in America, the gas is made intermittently in 
the usual way. The producer-gas is passed into a regenerator 
— a fire-brick chamber parted with a chequer-work of fire- 
brick — and is there burnt. When the producer is reversed 
for water-gas making, the steam is blown through this 
chamber, and therefore becomes intensely hot before it 
enters the top of the producer. A stream of coal-dust is 
also blown into the top of the producer, and the products of 
distillation pass downwards through the fuel with the hot 
steam, and are broken up into permanent gases and fixed 
carbon. As soon as steam passes through undecomposed 
the process is reversed. 

The Dellwik - Fleischer Process. — In all the earlier 
types of water-gas producer the carbon was only burnt to 
carbon monoxide, and as this evolves only a small amount 
of heat, the heating-up stage was very long. During this 
stage a combustible gas was evolved, but as a rule no use 
could be made of this. In the process devised by Messrs. 
Dellwik-Fleischer the fuel during the heating-up stage is 
burnt to carbon dioxide, so that a large amount of heat is 
evolved and the heating-up stage is much shortened. 

1 J.I. and S.I., 1890, vol. ii. p. 280. 



GASEOUS FUEL 185 

Almost any form of producer might be used, but that 
adopted by Messrs. Dellwik-Fleiseher is a simple bar-bottom 
producer up to 12 feet in diameter and 14 feet high. The 
only essential is that the layer of fuel must be thin, usually 
not more than 3 feet thick, and that a large quantity of air 
must be supplied so as to ensure complete and rapid com- 
bustion. To start the producer the fire is lighted, coke is 
put in from a hopper above, and air is blown in, the products 
of combustion passing away by a chimney. As soon as the 
coke is hot enough, the air is turned off and steam is blown 
in, the gas being led away to a gas-holder. As soon as the 
temperature is so low that a large quantity of steam is 
escaping undecomposed, which is determined by means of a 
test cock, the gas and steam valves are closed and air is again 
blown in. The heating up occupies only two or three 
minutes, and gas is made for about eight or ten minutes. 

The hot gas on its way to the gas-holder passes through 
a superheater, so that its sensible heat is partially used in 
heating the steam, and the plant is so arranged that the 
steam can be blown in alternately above and below the fuel. 
About 4 cwt. of coke is added after every second blow. 
Mr. Dellwik thus describes the theory of the process : 1 

" If we look into the chemical reactions in the formation 
of water-gas we find that 18 lb. of steam, consisting of 2 lb. 
of hydrogen and 16 lb. of oxygen, require for their decom- 
position 2x28780=57560 thermal units. The 16 lb. of 
oxygen combines with 12 lb. of carbon to form 28 lb. of 
carbon monoxide, which in mixture with the 2 lb. of hydro- 
gen form 30 lb. =753-4 cubic feet of water-gas. The heat 
developed by the formation of the carbon monoxide is 
12x2400=28800 thermal units, thus leaving a balance of 
57560 - 28800 =28760 thermal units, which must be replaced 
by the combustion of carbon during the blows. Assuming 
then, as is approximately the case in practice, that the blow- 
gas leaves the generator at a temperature of 700° C, we 
find: 

1 J.I. and S.I., 1900, vol. i. p. 123. 



186 



FUEL 



Old Method. 



New Method. 



1 lb. of C requires for combustion . 

The O is accompanied by 

And the products of combustion 

carry with them at 700° C. . 
The heat of combustion of 1 lb. of 

C is 

Balance available for heating is . 1 

To fill the before -mentioned balance"! 
of 28760 Th.U., in the production [ 
of 30 lb. of gas, there must be i 
burnt J 

Not counting the heat lost by radia-^l 
tion and other causes, there are I 
required for the production of 30 j 
lb. =753 cu. ft. of water-gas J 

Per lb. of C are obtained . . -j 

As water-gas of the theoreticaH 
composition contains 167 Th.U. [ 
per cubic foot, there are utilized j 
in the water-gas per 1 lb. of C J 



to CO y| lb. O. 
4-32 lb. N. 

1136 Th.U. 

2400 Th.U. 
2400-1136 
= 1264 Th.U. 

28760 



1264 
= 22-75 lb. C. 

12+22-75 
= 34-75 lb. C. 

21-7 cu. ft. of 

water-gas 
3627 Th.U. = 
44-8 per cent 
of the heating 
value of the C. 



to C0 2 |§ lb. O. 

8-66 lb. N. 



2092 Th.U. 

8080 Th.U. 
8080 - 2092 
= 5988 Th.U. 



28760 
5988 



4-83 lb. C. 



12+4-83 
= 16-83 lb. C. 

44-7 cu. ft. of 
water-gas. 

7465 Th.U. = 
92-5 per cent 
of the heating 
value of the C. 



In this it is assumed that all the carbon in the heating -up 
stage is burnt to carbon dioxide. This is very rarely the 
case, but the products of combustion only contain about 
1 per cent of carbon monoxide. 

In practice the efficiency has been found to be in some 
cases as high as 80 per cent. 

Fig. 50 illustrates the duplex generator of the Kramer 
and Aarts (K. & A.) system, and Fig. 51 another modification 
of the same, showing combined generator and carburettor. 

Nature of Water-gas. — Water-gas has a much higher 
calorific power than producer-gas, as will be seen from the 
following figures, where we assume an average quality made 
from gas coke : 





Per cent. 






By volume. 


B.Th.U. per cubic fool 


Carbon dioxide 


4 




Oxygen 


1 




Carbon monoxide . 


. 38 


0-38x320 = 121-6 


Hydrogen 


. 50 


0-50 x 321 = 160-5 


Nitrogen 


7 


•• 



100 



282-1 



GASEOUS FUEL 



187 



1000 cubic feet of water-gas will therefore evolve on com- 
bustion about twice as much heat as enriched producer-gas 
and three times as much as simple producer-gas. 




GAS 



STEA 



STEAM 



Fig. 50. — K. & A. Water-gas Generator. 

As it is comparatively low in content of carbon dioxide 
and nitrogen, water-gas is well suited for use where a high 
temperature is required to be attained quickly. It burns 
with a non-luminous flame, but it may be used for in- 



188 



FUEL 



candescent lighting, or it may be made luminous by making 
it take up some volatile hydrocarbon. If acetylene could be 



OUTLET TO STACKS. 
ALSO STEAM. OIL.ANO 
CIRCULATING GAS INLET. 




Fig. 51. — Ferry Water-gas Generator. 



produced at a cheap rate, it should be easy to make a good 
luminous gas by mixing water-gas with it. 



GASEOUS FUEL 189 

Water-gas is very poisonous and is odourless, and several 
accidents have happened by the non-detection of escapes ; 
to obviate this danger the gas is sometimes mixed with some 
strong-smelling volatile body such as carbon disulphide. 

The great objection to water-gas is the necessity for 
making it intermittently, so that gas-holders are necessary. 

Carburetted Water - gas. — Very large quantities of 
carburetted water-gas have been made in this country, and 
still greater quantities in the United States, to meet the 
demand for iUuminating gas and the enrichment of coal-gas. 
The water-gas is carburetted by spraying petroleum or 
heavy paraffin oil on to red-hot brick chequer-work during 
the " run " in the manufacture of water-gas. The quantity 
of oil necessary varies from 2 to 4 gallons per thousand cubic 
feet of total gas made, according to the quality (candle- 
power and calorific value) required. Over 60,000,000 
gallons of oil have been used annually in the United King- 
dom for this purpose. Owing, however, to the relegation 
of the candle-power in town gas to a position of second- 
ary importance, there is now a much lower consumption 
of oil. 

The " Economical " plant used in many gasworks con- 
sisted essentially of three chambers, generator, carburettor, 
and superheater, as in Fig. 52. In the " Humphries and 
Glasgow " system the superheater is superimposed on the 
carburettor. In both cases the brickwork of the carburettor 
and superheater is rendered red-hot partly by the sensible 
heat of the gases coming from the generator and partly by 
the combustion of a portion of the producer-gas made in the 
generator during the " blow," and the temperature is capable 
of being suitably controlled. 

Oil-gas. — This gas is made by the destructive distil- 
lation of oil, that is "cracking," at a high temperature, 
with or without the use of steam. It is almost entirely 
used for lighting purposes, but has been tried for furnace 
use. In the Archer process " steam superheated to about 
1000° F. is made to pass through an injector and draw 



190 



FUEL 



with it a quantity of oil which becomes mixed with the 
steam. The mixture is further heated to about 1300° F., 
when it receives an additional quantity of oil ; and finally 
the mixture is heated to 2400° F., whereby it is con- 
verted into permanent gas." Gas made by this process 
is called water-oil-gas. In the Pintsch, and some other 
processes, the oil is gasified by being allowed to drop into 
red-hot retorts. 



Value 



ISt/kk\ 



Superheater 



Generator 

O PEXATtNG 



Coke 




ro ebA/OEAtSEPS 



lyx/v^y/^y/v 



Fig. 52. — Section of Carburetteft Water-gas Plant. 



The yield of gas varies very much, but it may be 
taken as being from 80 to 150 cubic feet per gallon of oil, 
or about 22,000 to 42,000 cubic feet per ton — the higher 
quantities only when steam is used with the oil ; and at 
the same time there is a considerable quantity of liquid 
residue. 

An average oil-gas contains 25 per cent by volume of 
hydrogen, 45 per cent methane, and 30 per cent of heavy 
hydrocarbons, and possesses a calorific value of about 1050 
B.Th.U. per cubic foot, gross. 



GASEOUS FUEL 



191 



Carbon Dioxide, C0 2 . . . 
Heavy Hydrocarbons, Cm Hn 

Oxygen, O 

Carbon Monoxide, CO . . . 

Hydrogen, H 

Methane, CH 4 

Nitrogen, N 






a u <6 
a a> m 

O o 



25 



69 



c3 S cS 



g£ 



52 






16 



hJS' 



Composition of Various Gases. — The analyses on p. 192 
will give a good idea of the nature of the gases used as fuels. 1 

The approximate composition of the more important 
industrial gases is given in the above table. 

Advantages of Gaseous Fuel : 

1. The supply of both air and gas is under control, so that 
any required temperature can be maintained with perfect 
regularity for any time ; and also the nature of the flame 
can be regulated, so that it can be made oxidizing, reducing, 
or neutral, as required. 

2. Perfect combustion can be maintained with a very 
slight excess of air over that theoretically required, and no 
smoke need be produced. 

3. Much higher temperatures can be attained than is 
possible with solid fuel, as both air and gases can be heated 
to a high temperature by means of regenerators before 
combustion. 

4. Changes of temperature being less, the furnaces, etc., 
will last longer. 

5. A commoner quality of fuel can be used. 

6. The great ease with which the gas can be conveyed in 
pipes to any part of the works required, all the solid fuel 



1 Nos. 1 to 21 are from a paper by Mr. G. Ritchie, read before the 
West of Scotland Iron and Steel Institute. Author is Mr. Ritchie, 



192 



FUEL 



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Pi 
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& 

§ 

M 

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i-hearth 

do. do. 

gas from Coke .... 
it 

'-gas 

do. 

Coal-fed . . . . . 
ce Generator 


1. Ebelmann's 

2. Do. 

3. Do. 

4. Siemens Opei 

5. Do. Close 

6. Do. 

7. Do. 

8. Wilson . 

9. Do. . 

10. Do. . 

11. Do. . 

12. Ingham . 

13. Do. . 

14. Do. . 

15. Dowson . 

16. Essen Water- 

17. "Lowe" Wa 

18. Gas from Pee 

19. " Thwaite " < 

20. Natural Gas 

21. Do. 

22. Strong Watei 

23. Siemens Clos< 

24. Do. 

25. With large 63 

26. Blast-furnace 

27. Gas from Cht 

28. Gas from Col 



BY-PRODUCTS 193 

being delivered at the producers placed conveniently for the 
purpose. 

7. The gas can be used directly for the production of 
energy in a gas-engine. 

The disadvantages are : 

1. Danger of explosion. This is of no importance, as 
accidents are easily prevented. 

2. The flame of many of the gases being only slightly 
luminous, its radiative power is not very high. 



CHAPTER VIII 

BY-PRODUCTS AND LOW-TEMPERATURE CARBONIZATION 

Recovery of By-products. — It has now become general 
practice to aim at recovering tar, ammonia, and crude benzole 
from the gas made in coke-ovens, producers, and blast- 
furnaces wherever possible. 

In many cases it has not been profitable in the past to 
carry out the whole recovery process owing to various 
difficulties. 

While all coke-oven plants and gasworks can, and for 
the most part do, quite readily recover tar and ammonia very 
completely in a readily utilizable condition, the tar made by 
producers is accompanied, as a rule, by so much steam and 
is so constituted that it condenses in a partly emulsified 
condition containing on an average, say, 40 per cent of 
water, which is difficult to remove, and whose removal is 
absolutely necessary to make it fit for the ordinary purposes 
of tar. 

Again, gas producers, as a rule, do not yield anything but 
the merest trace of ammonia. In ordex to recover ammonia 
it is necessary to at least double the proportion of steam fed 
to the producer along with the air-blast. For example, the 
Mond producers generally require 1 lb. of steam per lb. of 
coal gasified when working under non>*reeov§ry (no ammonia) 

(D107) o 



194 FUEL 

conditions, whereas 2 \ lb. of steam are required when it is 
desired to cause the evolution of ammonia in profitable 
quantities. 

The question as to whether it will be a paying proposition 
to make the ammonia at the expense of the steam is one that 
can only be settled by considering the particular circum- 
stances of each individual case. Fortunately the pressure of 
steam required is only 2 or 3 lb. per square inch, and exhaust 
steam can therefore be utilized. 

If, therefore, there is a large available supply of exhaust 
steam going to waste in connection with steam - engines 
already installed in a works, such as those driving exhausters, 
pumps, electric generators, air compressors, etc., the problem 
is simplified and the probability will be a saving of about 
four shillings, on a pre-war basis, per ton of coal gasified after 
allowing for all charges. 

In such a case, or designedly so, the steam is used for a 
double purpose — to drive the engines at high pressure under 
non -condensing conditions and afterwards to supply the pro- 
ducers. The engines act like so many reducing valves or 
governors. 

When, however, we are considering an entirely new 
industry or plant we cannot in fairness present free steam 
to the producer plant, but must take into account the probably 
well-recognized fact that in a modern works, especially having 
regard to present high prices of fuel, it would be most wasteful 
to instal non-condensing engines of any kind if there were no 
producer plant to consider. The price of steam to be charged 
to the producer plant is in this case determined by the 
difference in steam consumption between condensing con- 
ditions on the one hand and non-condensing conditions on 
the other. As 12 lb. and 36 lb. may be taken as represent- 
ing the consumption of steam per brake-horse-power hour 
for condensing and non-condensing engines respectively, we 
may assume a fair charge for steam supplied to the producers 
would be between 60 and 70 per cent of the actual cost as 
delivered from the boilers, 



BY-PRODUCTS 195 

The cost of sulphuric acid and the market price of sulphate 
of ammonia are the other principal factors that govern a 
decision of this question. The recovery of 90 lb. of sulphate 
of ammonia, worth about 14s. per ton of coal, would appear 
to be a most attractive proposition, and from a national point 
of view a very desirable one, and it is a duty to give it fair 
consideration in every case, even though it does entail very 
considerable additional capital outlay. 

While the extraction of crude benzole from coke-oven gas 
is very general and profitable, there are not very many gas- 
works which now take the trouble to wash out the light spirit 
from coal-gas, although a large number of the larger works 
were obliged to do so to augment the supplies of benzene and 
toluene for high explosives manufacture during the war. 
Whether it is profitable to do so or not depends chiefly on the 
relative values of the therm (100,000 B.Th.U.) and motor 
spirit. At the end of the year 1920 the therm in London 
gas costs about lOd. ; in petrol at 4s. per gallon it costs about 
33d. There is in this case a good margin of profit, but with 
petrol at 2s. per gallon there would cease to be sufficient 
margin in most cases. 

Coke-oven gas, though differing in no essential feature 
from ordinary town gas, cannot be sold at the same price 
per therm as town gas, because there is no outlet for it except 
in certain favoured places like Middlesbrough and Sheffield, 
where it is purified from sulphuretted hydrogen and sold as 
town gas. It is therefore worth little more than its heating 
value compared with coal, which at 30s. per ton represents a 
cost of not more than 1 Jd. per therm. Assuming a moderate 
yield of benzole — a minimum of, say, one gallon per ton of 
coal — it would probably be still profitable to recover benzole 
from coke-oven gas even if motor spirit dropped in price to 
Is. 3d. per gallon, coal remaining at 30s. 

Tar. — The yield of tar from the ordinary carbonization 
of coal varies from 8 to 15 gallons per ton according to the 
nature of the coal and the system of carbonization. It is 
greatest with vertical retorts where steaming of the charge is 



196 FUEL 

practised, and least with horizontal retorts having only one 
ascension pipe working at the highest possible temperatures. 
In the latter case the tar is particularly well cracked, with the 
result that the gas yield is increased but the tar is diminished 
and contains a large amount of free carbon. Bituminous 
coals, high in volatile matter, give the best yields. Probably 
the richest Yorkshire coals take the lead in this respect, 
though, of course, they are greatly surpassed by the various 
cannels, which, as a rule, yield at least 20 gallons of tar 
per ton. 

Not only does the production vary with different coals 
and systems of retorting, but also the composition or quality 
shows marked variations. While coke-ovens, horizontal and 
inclined retorts, and chamber ovens are pretty much alike in 
the content of middle and heavy oils, naphthalene and pitch, 
vertical retorts give a much larger proportion of middle and 
heavy oils, much less naphthalene and pitch, this pitch 
containing only a small percentage of free carbon. 

The proportion of light oils, distilling up to 170° C, to be 
found in different tars is subject to very great variation, even 
when the same system of retorting, the same temperature of 
carbonization, and the same coal are considered. The differ- 
ence may be due entirely to the conditions of condensation 
which allow more or less light oils to be retained in the gas 
according to whether the cooling is sudden or gradual, or 
whether the tar is circulated in contact with the gas or not. 
It is worthy of special note that coal-gas made from a ton of 
coal retains in the cold state, after removal of all the tar, 
from ten to forty times as much benzene as is to be found 
in the tar made from the same quantity of coal. Generally 
speaking, when the yield of gas is comparatively large the 
percentage of light oil left in the tar will be low. 

The amount of water or ammoniacal liquor to be found 
in tar is seldom less than 2 per cent, and may, in emulsions, 
be as high as 80 per cent, when the problem of separation 
becomes a serious one. 

Ordinary coal-tar made in gasworks and coke-oven works 






BY-PRODUCTS 197 

gives very little trouble as a rule with regard to the water 
content, a long period of settlement, preferably in a warm 
state in underground wells, being sufficient to enable the 
water to rise to the top and any sediment to sink to the 
bottom. But cases are known where, owing to its rapid 
circulation in the hydraulic mains of coke-oven installations 
— necessary in order to keep down pitch deposits — the tar 
partly emulsifies and may contain 40 or 50 per cent of water. 
The difficulty and cost of removal of the water makes the tar 
almost worthless to the ordinary tar distiller. 

The worst cases of tar emulsion are, however, to be found 
in the manufacture of carburetted water-gas and producer- 
gas, and special means have to be sought to dehydrate or 
distil the product, even if there be no balance of profit in the 
operation, because, as a rule, it is impossible to dispose of the 
emulsion into a river, canal, or pit. 

The plant required for the collection and removal of tar 
made from the distillation of coal is simple and the cost is 
low. In general, the hot gases enter a cooling main pipe, 
hydraulic main or foul main, in which tar or ammoniacal 
liquor is circulated ; then follow atmospheric condensers, 
water-cooled condensers, and a final tar extractor of some 
kind. The Pelouze and Audouin tar extractor, the Livesey 
washer, Cyclone extractors and centrifugal fan extractors 
are the principal apparatus in use for this purpose. The tar 
recovered hot is naturally heavier in specific gravity and 
higher in boiling-point than the tar obtained from the final 
extractor. 

The removal of tar from producer-gas is a much more 
difficult problem. In many cases it has been found more 
profitable to allow the gas to carry most of the tar in the hot 
state direct to the furnaces, not only because of the difficulty 
of tar removal, but also because of the increased calorific value 
of the supply. 

It has sometimes been found, in steelworks especially, that 
a tarless gas does not effect a sufficiently high temperature. 

In cases where there is ammonia recovery and the gas is 



198 



FUEL 



necessarily cooled, the bulk of the tar is thrown down and has 
to be dealt with. Tar mist in producer-gas is, however, very 
persistent and travels many miles when the velocity is high. 
Washers, centrifugal fans, and woodwool or sawdust purifier 
boxes have to be brought into requisition to make the gas 
suitable for furnace work, such as firing coke-ovens and for 
gas-engines. The tar collected is very viscous and difficult 
to handle unless kept hot by closed steam-pipes. It usually 
contains about 40 per cent of water and must be dehydrated 
or distilled in situ. 

It is dehydrated by agitation at a temperature of about 
95° maintained by closed steam coils for two days, or it may 
be distilled in vacuo. By the former method there is a slight 
loss of creosote and the only product is an inferior pitch. 
By the latter a good yield of creosote and a good hard dry 
pitch are obtained. 

Producer -gas contains not more than 0-1 per cent of 
benzene vapour or its equivalent as against about 1 per cent 
in ordinary coal-gas. It is thus able to retain all the light 
spirit made in the producer. In a similar way it carries 
middle oils which would have condensed with the heavy 
tars were their vapours not so diluted by the large volume 
of gas. 

It is not easy to obtain reliable data of the composition 
of different varieties of coal-gas tar, but an average analysis 
on first distillation is as follows : 



Distilling 

Temperature. 

°C. 


Sp. 
Gr. 


Fraction. 


Per 

Cent. 


Commercial Products. 


0°-170° 

170°-230° 

230°-270° 

270°-350° 

Above 350° 


0-94 

0-98 
104 

1-08 


Light oils 
(crude naphtha) 

Middle oils 
(carbolic oil) 

Heavy oils 

(creosote oil) 

Anthracene oil 

Pitch 


3 

17 
10 
15 
55 
100 


Benzole for motor spirit, dyes, and 
other chemicals, solvent and burn- 
ing naphtha. 

Naphthalene, carbolic acid, creosote. 

Creosote, lubricating oil, wash oil, 
fuel oil. 

Anthracene, wash oil, fuel oil, lubri- 
cating oil. 

For briquetting, varnishes, cements, 
asphalt, road-spraying, and fuel. 



The ultimate products when purified are approximately 



BY-PRODUCTS 199 

Per Cent. 
Benzene. ...... 1 

Toluene. ...... £ 

Xylene .' j 

Phenol (carbolic acid) .... £ 

Cresylic acid . . . . . . If 

Naphthalene ...... 8 

Pyridine ...... J 

Anthracene ...... 2 

Middle and heavy oils . . . .31 

Pitch . 55 

100 

Ammonia. — In ordinary gasworks or coke-oven practice 
half the ammonia collects in the condensate along with the 
tar, and half is obtained by washing the gas in specially 
designed apparatus. 

The former is usually called the virgin liquor and contains 
nearly all the fixed ammonia salts — chloride and sulphate 
principally. It separates out readily from the heavier tar. 
With ordinary dry coal the virgin liquor amounts to about 
15 gallons per ton, but when water is added to the coal to 
aid compressing this figure may be doubled. 

The ammonia retained by the cooled gas is generally 
removed by two washers or ^ets of washers or scrubbers. 
For example, a washer with a very efficient bubbling action 
like the Livesey washer may be used to serve the double 
purpose of removing tar and ammonia, while the final 
apparatus, which has the more difficult work of removing 
the last traces of ammonia, is of special design, and is fed 
with a minimum quantity of cold wash water, a minimum 
quantity being used so as not to reduce the strength of the 
ammoniacal liquor and make the subsequent distillation of 
the ammonia more costly. As the final type of washer, tower 
scrubbers filled with coke or wooden boards set on edge were 
formerly very largely used, but are being replaced more and 
more by mechanical appliances, such as the Holmes hori- 
zontal brush washer or vertical centrifugal spraying machines, 
where the extraction is carried out very efficiently by 
systematic stage washing. 



200 FUEL 

Many coke-oven plants use the system of direct recovery 
of ammonia. The gas is deprived as completely as possible 
of its tar while still hot, and is then subjected to washing 
with sulphuric acid in lead-lined vessels, solid sulphate of 
ammonia being obtained directly. In the Otto-Hilgenstock 
process there is an ingenious system of tar removal from the 
hot gas by means of tar jets. 

The ammonia in producer-gas is accompanied by so much 
steam that any process of recovery as ammoniacal liquor 
(aqueous solution) must fail owing to the low concentration 
possible. In this case it is quite necessary to employ the 
direct recovery method. The Power Gas Corporation, who 
supply Mond gas plants, have made use of tower scrubbers, 
and mechanical dash washers either in cast iron or lead, for 
this purpose. 

Benzole. — About 30,000,000 gallons of benzole are 
recovered annually by the by-product coke-ovens of the 
United Kingdom. The crude benzole at first obtained is 
subjected to fractional distillation. The portion distilling 
below 100° C, forming the great bulk of the product, is 
usually washed with concentrated sulphuric acid for removal 
of thiophene. and unsaturated hydrocarbons, thereby reduc- 
ing the sulphur content and otherwise purifying the spirit. 
On again distilling pure benzene may be obtained. Only a 
small proportion of the benzene contained in the crude 
benzole is required in this country for chemical purposes, 
such as the manufacture of nitrobenzene, aniline, and dye- 
stuffs ; Germany is said to consume annually about 30,000,000 
gallons in this way. The chief outlet for this valuable light 
oil is as motor spirit. A small proportion — about 15 per 
cent — of the total consists of toluene, which is usually sold in 
what is known as 90's benzole, but was carefully separated 
by fractionation during the war for the manufacture of the 
high explosive trinitrotoluene (T.N.T.), as was also benzene 
itself for making synthetic phenol and hence picric acid 
(lyddite). Toluene is also used fairly largely in the dye- 
stuffs industry. 



BY-PRODUCTS 201 

The higher fractions consist principally of xylene, and 
find their principal use as solvent and burning naphtha. 

The process of benzole extraction consists in washing the 
gas with a suitable heavy oil — creosote or anthracene oil — at 
the rate of about 100 gallons of wash oil per ton of coal 
carbonized. The benzolized oil thus obtained generally 
contains about 2| per cent of benzole. It is preheated and 
run down through a " stripping " still, where it meets live 
steam, which disengages almost the whole of the light spirit 
from the heavy oil. The vapours of steam and light spirit 
passing away together are condensed to water and liquid 
benzole respectively, and continuously separated. The 
stripped oil is cooled and returned to the washers for further 
use. It can be used over and over again almost indefinitely 
so long as it is freed from accumulations of naphthalene or 
heavy tar or water, which interfere with its efficiency. The 
washing efficiency is considered satisfactory at 90 per cent. 
It is essential to cool both gas and oil to a temperature of not 
more than about 70° F. to obtain the best results. 

There is probably quite as much light spirit produced 
from a ton of coal when gasified in a gas producer as there is 
when the coal is carbonized. But it is useless to attempt to 
wash it out with heavy oil, because the vapours of the light 
spirit are diluted ten times and must therefore escape re- 
covery, the washing process being a purely physical one 
depending on solubility and vapour tension, and not on 
chemical affinity. 

The same type of plant is used for oil washing as for 
ammonia extraction by means of water, and here, too, the 
old-fashioned cumbersome tower scrubbers are giving way 
to the more efficient, compact, mechanical washers, particu- 
larly those of the vertical centrifugal type. 

Coke-ovens, horizontal and inclined retorts, and chamber 
ovens give the highest yield of benzole. Vertical retorts 
give a smaller yield of light spirit, and a considerable pro- 
portion of it is " paraffinoid " and not of the "aromatic" 
series of hydrocarbons (benzene series). 



202 FUEL 

Ethylene and Alcohol from Coke-oven Gas. — Mr. 
Ernest Bury of the Skinningrove Iron Company has during 
the war opened up the question of extracting the 2 per cent 
by volume of ethylene (C 2 H 4 ) to be found in coke-oven gas. 
This can be absorbed as such by charcoal, but probably not 
in an economic way, and the method proposed and actually 
worked on a small scale is to wash the gas, purified from 
sulphuretted hydrogen and dried, with concentrated sul- 
phuric acid at 60-70° C, and subject the resulting ethyl- 
hydrogen sulphate (sulphovinic acid) to hydrolysis and dis- 
tillation in a current of steam with the production of weak 
alcohol, which is further purified by redistillation. 

It would be possible to produce about 30,000,000 gallons 
of pure alcohol annually from the coke-ovens now engaged 
in benzole recovery and thus make an important contribution 
to the supply of motor spirit, of which about 150,000,000 
gallons are required every year by this country alone. 

It is, however, not yet clear that the process will be a 
commercial success. 

Potash Salts from Blast-furnace Gas. — It has long 
been known that the dust contained in blast-furnace gas 
contains a large proportion — in the neighbourhood of 20 per 
cent — of potassium compounds, chiefly chloride. Potassium 
in its various forms is a valuable manure, and is also required 
in the glass industry. Certain quantities have been re- 
covered by washing with water at some works. A large 
plant has been erected at Skinningrove by the Lodge Fume 
Deposit Company, on the principle of electrostatic precipita- 
tion of the dust from the hot gas, the very high voltage of 
about 50,000 being employed for the purpose with an 
efficiency of deposition of over 80 per cent. 

Low-temperature Carbonization. — Much has been said 
and written on the subject of the distillation of coal at low 
temperatures during the last twenty years. It is largely 
due to the company promoter, however, that the man in the 
street owes his knowledge of smokeless fuel, the value of 
which has been extolled to the skies. There is nothing to 



LOW-TEMPERATURE CARBONIZATION 203 

find fault with in regard to the advocacy of replacing raw 
coal by fuel that will not produce the direct nuisance of 
smoke and the secondary one of fog, evils that owe their 
origin very largely to the burning of coal in fire-grates both 
in the house and in the factory. It was no doubt the fancy 
price which it was hoped would be obtained for a smokeless 
solid fuel that acted as chief incentive to the pioneers of these 
processes in the first instance. Latterly the question of tar 
oils has loomed largely into view, and at the present time 
probably claims the place of greatest importance. 

About forty years ago it was general practice to employ 
cast-iron retorts for coal-gas manufacture. With these it 
was not advisable to exceed a temperature of 1650° F., other- 
wise the retort had too short a life to be economical. Retorts 
in those days all worked intermittently — a charge of coal 
was thrown into the retort and withdrawn at the end of, 
say, six hours, by which time it attained throughout its 
mass a temperature of 1600°. The gas yield was com- 
paratively small, but the quality was good. The gas was 
rich in heavy hydrocarbons, such as ethylene and benzene. 
To these constituents it owed its high candle-power. It 
contained a high percentage — at least 35 per cent — of 
methane, and to this it owed the largest proportion of its 
heating value. The yield of tar was considerably greater 
than is now usual in carbonizing practice, and the quality of 
the same was superior to the present-day product in that it 
was thinner, contained more light spirit, less naphthalene, 
less pitch, and much less free carbon. The yield of ammonia 
at 1650° F. was very good though not the best possible, this 
being at a maximum, probably at a carbonizing temperature 
of 1750° F., but it was distinctly better than can be obtained 
at the modern temperatures of 1900°-2000° F., vertical 
retorts excepted. There was an increase in the content of 
sulphuretted hydrogen and carbon dioxide in the gas, but a 
large reduction in organic sulphur compounds (carbon 
disulphide principally). A further feature of the conditions 
of gas manufacture and supply forty years ago was the 



204 FUEL 

almost total absence of naphthalene trouble, the main cause 
of stoppages in the gas services. 

In the early days of " Coalite " the advocates of the 
process based their calculations and hopes on the selling of 
coalite at a high figure which could only be realized by the 
conversion of a multitude of consumers to the religion of 
smoke abatement and abhorrence of the use of raw coal. 
There was probably a miscalculation in estimating that the 
whole of the coke would be available for sale at a high 
price ; allowance was not made for the friable nature of 
coalite, and the large amount of breeze produced in hand- 
ling and breaking up, such breeze commanding a very poor 
market. On account of these circumstances and unforeseen 
difficulties in carbonization, and lack of assistance by ex- 
perienced gas engineers, the early efforts to make the coalite 
process a commercial success signally failed. 

At the present time when fuel of all kinds fetches high 
prices, and oils especially are at a premium, there is certainly 
a better field for the activities of low-temperature car- 
bonization. 

As a commercial proposition much depends in the first 
place on the prices to be obtained for the tar oils and motor 
spirit, and, in the second place, on the cost of carbonization, 
that is, the capital charges, wages, and fuel costs incidental to 
the process. Given a high return for specially valuable oils 
and a very large through-put per retort and per man, there is 
great hope that low temperature may be successfully adopted 
to recover the bulk of the volatile matter contained in our 
bituminous and semi-bituminous coals, now going in large 
measure to waste. One of the great difficulties in making 
coalite is to effect uniform carbonization. When made in 
the ordinary type of horizontal retort in layers 7 or 8 inches 
thick, the portions of the coal coming in contact with the 
retort and also the upper surfaces exposed to the radiant heat 
from the crown and upper sides of the retort are carbonized 
in much greater degree than the centre portions. The 
thicker the charge the poorer the result, owing to the very 



LOW-TEMPERATURE CARBONIZATION 205 

slow transmission of heat at low temperatures, and if very 
thin charges are used the output per retort is much reduced. 
When the convenient arrangements of vertical retorts are 
taken advantage of, " sticking " becomes a bugbear, and a 
careful selection of coals and a suitable special design of 
retort are then rendered essential. The difficulty is almost 
entirely one of retorting, and many designs and processes 
have been devised and patented to overcome this. 

The history of the process as gleaned from the technical 
literature written on the subject is briefly as follows : As 
early as 1681 a patent was taken out by Becker and Serle for 
carbonizing coal to produce pitch, tar, and smokeless fuel, and 
in 1781 the Earl of Dundonald brought out an improvement 
on this. As one of the first of modern efforts in this direction 
the English Patent, 67, 1890, by Parker, is noteworthy. In 
this process it was proposed to produce smokeless fuel by 
distilling the coal in a current of steam, water-gas, or coal-gas 
superheated to a temperature of 600° to 650° C. 

In 1906 the principal Coalite patent was taken out by 
Parker (Eng. Pat. 14,365 ; 1906). This consisted in dis- 
tilling coal in the presence of steam at a temperature not 
exceeding 800° F. (427° C). At first horizontal Q -shaped 
retorts, 5 feet wide, 7 feet long, and 16 inches high, were 
employed, the layer of coal being not more than 6 inches thick. 
Tapering cylindrical retorts and tubes of 6 inches diameter 
were subsequently used with only partial success. Nar- 
row vertical retorts of oblong cross-section were afterwards 
brought into use, and these in turn gave place to bunches of 
vertical tubes, 4 to 6 inches in diameter. Slots between the 
different tubes to relieve gas pressure were one of the more 
novel features. These arrangements were the subject of 
different patents. Internal heating by means of hot gases 
does not seem to have been developed to any extent by the 
Coalite company and its immediate successors. No definite 
carbonizing results have been published. The chief features 
of the process of " The Premier Tarless Fuel Ltd." are the 
very high vacuum and the special design of retort (Tozer). 



206 FUEL 

As high a vacuum as 20 to 27 inches of mercury (Simpson's 
process) is said to be capable of maintenance on a working 
scale and of producing improved yields of by-products. 
From the published description of the plant erected at 
Battersea one learns that their most recent design of vertical 
retort is cylindrical, 9 feet 5 inches long by 1 foot 8 inches 
in diameter, with an annular space divided by a central 
partition so as to give two carbonizing rings each containing 
four sections through the divisions created by vertical heat- 
transmitting ribs. The thickness of the charge of coal in 
each annulus is 2 J inches. The central space of the retort 
is empty, or rather contains hot air. Carbonization is con- 
ducted at 900° to 1000° F., the heating being external. The 
duration of charge is 3| to 4 hours. The bottom discharge 
doors are fitted with asbestos rings and are interlocking. 
The top mouthpieces are not partitioned ; when charging is 
in progress the central channel of each retort is sealed by a 
stopper. A bed consists of six retorts which take a com- 
bined charge of 2700 lb. of slack, equivalent to 50 tons per 
week. The retorts are encircled by firebrick and not ex- 
posed to direct gas heating, which is done by producer- 
gas at first and afterwards by a portion of the stripped 
gas made. 

The bed is divided into two chambers, three retorts in 
each. The gas goes to three condensing separators in series. 
These run off three different grades of tar, the pipes leading 
to the collecting tanks being at least 32 feet high to prevent 
condensate being drawn up and out by the high vacuum. 
A P. and A. tar extractor, constructed without seal and to 
stand a high vacuum, removes heavy tar oils. 

Next come the ammonia- washers, followed by the oil- 
washers for stripping the gas. The exhaust pump comes at 
the tail end. Before being sent to a holder the gas is com- 
pressed to 70 lb. per square inch and again suddenly ex- 
panded. On expansion a light spirit of a peculiar nature is 
said to separate out. Sample results from Yorkshire coals 
have been published as follows : 



LOW-TEMPERATURE CARBONIZATION 



207 



1. 


2. 


3. 


73 


73 


78 


9-2 


17-2 


22 


1-7 


11-5 


10-5 



Tarless fuel, per cent .... 
Tar (water-free), gallons per ton of coal . 
Sulphate of ammonia, lb. per ton of coal 

The gas yield is given as about 5800 cubic feet of a quality 
of 750 B.Th.U. (gross) before stripping, and 150 to 200 after. 
This remarkable drop in heating value, if correct, is difficult 
to account for. Quoting from Dr. C. Young's report published 
by the company, we learn that at a carbonizing temperature of 
900° to 1000° F., and a vacuum of 20 to 25 inches of mercury, 
the yields from a cannel and a bituminous coal were : 



Tarless Fuel, cwt. per ton 
Gas stripped to 300 B.Th.U. 

cubic feet per ton 
Sulphate, lb. per ton 
Tar (water-free), gals, per ton 
Light Spirit, gals, per ton by 

compressing and stripping gas 
Light Spirit in Tar (to 170° C), 

gals, per ton .... 
Total Light Spirit, gals, per ton 
Total Tar Oils, gals, per ton 
Pitch in above, lb. per ton . 



Cannel. 


Bituminous 




Coal. 


14 


14 


5000 


5000 


25-3 


23-8 


44 


22 


8-7 


2-2 


2-9 


1-3 


11-6 


3-5 


55-6 


25-5 


191 


90 



(For Comparison.) 
Best Yorkshire 
Coal at High 
Temperature. 



(13) 

(13,000) 
(30) 
(15) 

(3) 

(*) 

(H) 

(18*) 
(90) 



The coke obtained therefrom is described as dense but 
porous, not readily friable, easily ignited, giving a clear hot 
fire with good flame, but without smoke or soot. The tar 
oils produced had a specific gravity intermediate between 
shale oils and ordinary coal-tar. They are more closely 
allied to the former as they consist of paramnoid compounds 
and unsaturated hydrocarbons. Benzenoid hydrocarbons, 
such as naphthalene and anthracene, are entirely absent. 
The light oils are said to yield, in about equal quantities, 
solvent naphtha and a motor spirit resembling petrol rather 
than benzole, with a specific gravity of about 0-80. The 
middle oils, when fractionated, produce varying amounts of 
solar and fuel oils, The heavy oil is obtained as a crude 



208 FUEL 

lubricant, and the residue, amounting to 30 or 40 per cent, 
is a good hard pitch containing very little free carbon. 

An important point of difference from ordinary coal-tar 
is the large content (about 10 per cent) of tar acids, which 
consist almost entirely of cresylic acid and its homologues, 
and little or no phenol. 

Whether there are outstanding advantages in the use of 
a high vacuum is, to the writer's mind, rather doubtful. 
Heavy tars formed during the destructive distillation of the 
coal will certainly not be allowed to condense to the same 
extent on the cold coal as in other processes, and sticking 
will no doubt be thereby reduced. But we doubt if there is 
a greater yield of gas, tar, or oils than in other processes 
working at the same carbonizing temperature. There are 
the obvious disadvantages of increased costs of working and 
greater capital outlay, and danger of severe leakage and the 
attendant risk of explosive gas mixture. The process has 
yet to prove itself on a large scale. 

In the system adopted by the Barnsley Low-temperature 
Carbonization Company, fireclay takes the place of cast-iron. 
(Fireclay retorts would, of course, be quite out of the 
question in the Premier Tarless Company's process, on 
account of their porosity.) The retorts are vertical ovens, 
10 feet high by 10 feet long by 12 inches wide. Accord- 
ing to the Eng. Pat. 108,200, there are four zones of heat, 
starting with the base of the retort at 450° C, the next 
500°, the next 550°, and the free space at the top of the 
charge 900° to 1200°. The purpose of the high temperature 
at the top of the charge is to crack the tars, and this action 
is facilitated by suspending in the free space a grid of suitable 
shape and material. This kind of device was also adopted 
in the Woodall-Duckham high-temperature retort, but it 
probably has not a great deal of utility. The Barnsley 
method has also apparently followed that of the Woodall- 
Duckham company in having the highest temperature zone 
at the top of the retort. 

Definite results of the system have not been published. 



LOW-TEMPERATURE CARBONIZATION 209 

The carbonizing temperature is stated to be 600° C, the 
volatile matter left in the coke about 10 per cent, the yield 
of gas 6000 cubic feet, light spirit about 4 gallons, and tar 
about 18 gallons per ton of good gas coal. The ammonia 
yield is equivalent to about 15 lb. of sulphate per ton. 

Still another system of recent origin is that known as 
" Carbocoal " (Smith's patents), now working on a com- 
mercial scale in the United States. The process is a 
combination of low and high temperature carbonization. 
The finely crushed coal is first carbonized at 480° C. in 
horizontal retorts, where it is agitated by two slowly rotating 
paddles. The low- temperature coke automatically delivered 
as a spongy mass is briquetted with 8 to 10 per cent of 
pitch and then carbonized at 1090° C. in secondary retorts, 
which are of the inclined type. It is claimed that the yields 
of gas, tar, spirit, and ammonia are in excess of those 
obtained by other systems, while the resulting coke briquettes 
are hard, easily transported, and perfectly smokeless in 
burning. 

The Summers process, also of American origin (Eng. Pat. 
2069 and 10,284 of 1914), of compressing the coal while in a 
hot, semi-plastic state does not appear to have made much 
headway as yet. 

Various systems of internal heating have also been tried, 
with good prospects of ultimate success. The great draw- 
back to external heating is the small throughput and the 
consequent high capital outlay for retort plant. With a 
suitable method of intimate heat exchange between the mass 
of coal and a heating medium, one would imagine that the 
rate of distillation at a given temperature would be greatly 
speeded up ; and this is found to be the case in practice. 
In the McLaurin process (J.S.C.L, 1917, 620) the coal is 
carbonized in a current of hot producer gas. Some rather 
remarkable results of this process have been published. 
Coking coals are said to distil without showing any signs of 
intumescing. 

This is thought by Evans to be due to the oxygen present, 

( P 107 ) P 



210 FUEL 

although in small quantity, in the producer gas. McLaurin 
suggests that the rate of heating is the chief factor, and if it 
is too fast caking will ensue. In this process difficulties in 
passing the gas through are encountered, if the coal is very fine. 

The tars produced are remarkable in character, being 
readily separated into a resinous portion and tar oils by 
mixing them either with paraffin or weak sulphuric acid. 
(See McLaurin's patents 24,426, 1913, etc.) 

In the Chiswick (Del Monte) system we have an example 
of a continuous low-temperature process. 

In this case an Archimedean screw, revolving in a hori- 
zontal retort of circular section, keeps the fuel in motion and 
carries it along to the discharging end. 

In one modification of this system the screw was mounted 
on a hollow shaft, which could be heated internally by a row 
of gas jets, and a graduated temperature, instead of a uniform 
one, was maintained in the retort. This retort, however, is 
said to be unsuitable for caking coals, and can only be used 
for wood, shale, lignite, peat, cannel and non-caking coals. 

In the system of Pringle and Richards the coal is carried 
through a retort at about 500° C. by an endless conveyor, 
which is subdivided into compartments, each carrying its 
quota of coal. 

So far, the system has been tried only on a small scale, 
we understand, but it is said to offer prospects of ultimate 
success, the coke possessing superior qualities as a domestic 
fuel, being very porous and easily ignited. 

One of the most recent proposals is that of Swinburne, 
in which the inventor designs the retort for internal heating 
to a temperature of 350° C. by electric conductors. 

Another is to cause the powdered coal to fall in a shower 
down the inside of a retort heated with superheated steam 
or other inert gas. 

The process of Merz & M'Lellan, Michie & Weeks (Eng. 
Pat. 117,290, 118,777, 136,868, and 149,733), consists in the 
use of a vertical retort of large section, and the passage 
of a large volume of superheated steam upward through the 



LOW-TEMPERATURE CARBONIZATION 211 

charge of coal, which is preheated and fed continuously into 
the top of the retort. The coke is discharged continuously, 
as hot as possible, direct to the automatic stokers feeding the 
boilers. The coke is small, soft, and friable. The latent heat 
of the steam is recovered by heat - interchange with the 
boiler - feed water. The tar oils are separated from the 
condensate, and utilized partly for fuel, partly for special 
purposes, for which they command a high price. The gas 
is washed in the usual way for the recovery of light spirit, etc. 
Owing to the very large throughput attained, the low capital 
cost, and the low labour charges, it is not necessary to depend 
for commercial success on the problematic sale at a high 
figure of a household smokeless fuel. The process must be 
regarded as a distinct advance in the campaign against the 
use of raw coal as fuel. 

The advantages claimed for smokeless fuel over coal by 
Low Temperature Carbonization Ltd. are as follows : 

1. It radiates more heat into the room, the difference 
being very remarkable in large fires. 

2. It burns absolutely without smoke. 

3. It lights easily and burns up brightly at once, so that 
the fire is cheerful and efficient from the beginning. 

4. It keeps a clear glowing fire for many hours without 
attention. 

5. It can be burnt down into a very small fire without 
going out. 

6. It heats a room more cheaply than the best coal. 

7. It can be used in any form of grate or stove. 

8. Chimney and kitchen flues will not require sweeping. 
The validity of No. 6 will naturally depend on the 

respective prices of coalite and coal. 

There are, to the writer's mind, two essentials other than 
a suitable price necessary to the full success of a smokeless 
fuel in replacing coal in British grates. One is the proper 
sizing of the material, which should be uniformly of the size 
of a hen's egg. The other is the reduction of the ash 
content of the coal carbonized by some system of coal- 



212 FUEL 

washing. With these conditions observed even ordinary 
gas coke would be a welcome substitute for coal in house- 
hold grates. 



CHAPTER IX 

FURNACES FOR METALLURGICAL PURPOSES 

Classification of Furnaces. — It is very difficult to 
arrange a satisfactory classification of furnaces, (1) on 
account of the large number of forms that are in use, and 
(2) because the terms in common use are used so loosely 
that any attempt to give them a precise meaning is almost 
sure to fail. 

It is most convenient at the outset to divide furnaces into 
groups according to the nature of the fuel they are designed 
to use. 

1. Furnaces for solid fuel. 

2. Furnaces for liquid fuel. 

3. Furnaces for gaseous fuel. 

Furnaces for Solid Fuel. 

A. Furnaces in which the substance being heated is in 

contact with the fuel. 

1. The height is considerably greater than the 

diameter = Shaft furnaces. 
a No blast is used = Kilns. 
ft Blast is used = Blast furnaces. 

2, The height is not much greater than the 

diameter = Hearths, 

B. Furnaces in which the substance being heated is not 

mixed with the fuel, but is in contact with the 
products of combustion =Reverberatory furnaces. 
1. The charge is not melted. Roasting furnaces, 
a The hearth is fixed. 
fi The hearth rotates. 
£. The charge is melted. Melting furnaces. 



FURNACES FOR METALLURGICAL PURPOSES 213 

C. Furnaces in which the substance being heated is 
neither in contact with the fuel nor with the pro- 
ducts of combustion. 

1. The chamber in which the substance to be 

heated is fixed and is part of the furnace 
= Muffle furnaces. 

2. The chamber in which the substance to be 

heated is placed is movable and independent 
of the furnace = Crucible furnaces. 

3. The substance is volatilized and escapes in the 

form of vapour = Retort furnaces. 
Kilns. — These furnaces are used for many operations, in 
which a very high temperature is not required, as, for 
instance, the calcination of iron ore, lime-burning, and other 
similar purposes. They are made in a great variety of forms, 
according to the purpose for which they are to be used and 
the conditions under which they are to be worked. They 
are usually cylindrical in external form, and the interior is 
either cylindrical or conical. The charge mixed with the 
necessary amount of fuel is introduced at the top, and drawn 
in the solid condition at the bottom. Usually the charge 
rests on the solid floor of the kiln, and if the diameter is at 
all great an inner cone or wedge is used so as to throw the 
descending charge outwards and allow of its ready with- 
drawal, or in some cases the charge is made to rest on fire- 
bars. As the temperature required is not high the fuel 
consumption is small. In an iron-ore kiln, assuming that 
the ore contains no combustible material, the consumption 
is about f cwt. of coal per ton of ore, and in a good lime- 
kiln about 1 cwt. per ton of lime. When the substance 
being calcined contains combustible material, organic matter 
in the case of black-band iron-stones, or sulphur in the case 
of pyritous materials, no fuel may be necessary. As examples 
of kilns an ordinary Scotch iron-ore kiln and the Gjers kiln 
used for calcining iron ores in the Middlesborough district may 
be taken. These are sufficiently shown by the sectional draw- 
ings, Figs. 53 and 54, and no further description is necessary. 



2H 



FUEL 



As an example of a more complex kiln the Hoffman kiln 
may be taken. " It consists of a circular tunnel, which can 
be divided into any number of compartments, m 1} m 2 , etc., 
twelve or sixteen being the usual number. These compart- 
ments are, however, in direct communication with each 
other, except at one point where an iron plate pp 

placed across the tunnel 
interrupts the con- 
tinuity. This plate may 
be inserted through the 
roof of the tunnel down 
grooves provided for its 
reception in the walls. 
Each space between two 
sets of grooves is pro- 
vided with an internal 





Fig. 53. — Scotch Iron-ore Kiln. 



FiG. 54 — Gjers Kiln. 
C, Cone. P, P, Pillars, 
o, o, Lateral openings. 



flue n l9 n^ 



etc., which by the removal of a damper 
can be placed in communication with a central chimney, 
and each space has also a door bb in the outer wall. 
Only two of these doors are open at a time. The 
whole of the tunnel is kept full of the material " to be 
burned and the fuel, " except one compartment which is 
always empty. The position of the empty compartment 
varies from day to day. Let the plate occupy the position 



FURNACES FOR METALLURGICAL PURPOSES 215 

pp shown in Fig. 55. The newest material has been charged 
in behind it into the compartment 16. Air enters in front 
of it through the open door of the empty compartment 
No. 1, and through the door, also open, of the next com- 
partment, which contains finished material that has been 
longer in the furnace than the rest, and has but little heat 
to give up to the incoming current of air. This current 
is drawn by natural draught round the entire tunnel, and 
can only enter the chimney through one or more of the 
flues that have been opened behind the plate. After an 
interval of twenty-four hours from the last charging the 



FIG. 55.— Otto Hoffman Kiln. 

compartment No. 1 has been filled, and the position of the 
iron partition is shifted to the next groove to the right, and 
the compartment No. 2 in front of the plate is emptied. 
Thus new material is continually kept behind the plate and 
finished material in front of it. Air entering comes in contact 
with material which gradually increases in temperature, for 
it will be obvious that the position of the hottest part of the 
furnace must be continually travelling round the circle, and 
that in a number of days, corresponding with the number of 
compartments, the zone of combustion will have travelled 
completely round the circuit. The air and the material to 
be treated enter and leave the furnace in a cold condition, 
so that there can be no waste of heat provided that the 
adjustment of the dampers in the flues through which the 



216 FUEL 

gases pass to the chimney is carefully effected. In order to 
remedy local irregularities of combustion air may, if neces- 
sary, be admitted through suitable orifices in the roof." * 

The volume of each compartment may vary from 282 to 
1765 cubic feet, and the height of the tunnel should not 
exceed 9 feet. 

Owing to the small quantity of fuel used and the large 
amount of air admitted the atmosphere in a kiln is always 
oxidizing, so that the action is often roasting as well as 
calcining. 

The Blast - furnace. — The blast-furnace, though in 
general resembling a circular kiln, differs from it in important 
points. The air is forced in under pressure, a much larger 
quantity of fuel is used, and the temperature is so high that 
the charge is melted, and has to be tapped out in the liquid 
condition. 

The size and form of blast-furnaces varies enormously, 
from the large iron-smelting furnaces of Cleveland to the 
small furnaces, six feet or so in height, used for lead smelting. 
To illustrate the general character of the furnace and the 
mode of action two types will be briefly considered : the 
blast-furnace as used for iron smelting, and the smaller water- 
jacket furnaces used for lead smelting in Colorado. 

Iron-smelting blast-furnaces vary in height from 40 to 
100 feet, and the other dimensions vary similarly. An 
ordinary blast-furnace consists of three parts : an upper 
conical part or shaft, a middle part in the form of an inverted 
cone called the bosh, and a bottom cylindrical portion or 
hearth. These portions may be separated by distinct lines of 
demarcation, or they may curve gradually one into the other. 
Small blast-furnaces may be of the same diameter all the way 
down, or they may taper gradually from top to bottom. 
The ratio of height to greatest diameter may vary very much, 
but in modern furnaces is usually about 3-5 or 4 : 1, varying 
down to about 3 : 1 and up to 6 : 1 in very exceptional cases. 

The charge is introduced at the top, which is now 

1 Roberts-Austen, Introduction to the Study of Metallurgy. 



FURNACES FOR METALLURGICAL PURPOSES 217 



almost always provided with some form of charging ap- 
paratus by which the gases can be drawn off, since these 
are combustible and are therefore of value. Air is blown 
in by a series of tuyeres just at the top of the hearth, 
leaving space below for the accumulation of the molten slag 
and metal which are tapped out periodically from tap-holes 
in the hearth, one at a higher level for the slag and another 
at a lower level for the metal. 
The air is supplied from the 
blowing engines or fans by 
a blast - main which passes 
round the furnace. 

The chemical action which 
takes place in the blast- 
furnace is in the main simple. 
The oxygen of the air coming 
in contact with the fuel at a 
high temperature is at once 
converted into carbon mon- 
oxide. If by chance any 
carbon dioxide should be 
formed, it would be instantly 
reduced, so that the gas as it 
ascends will consist essentially 
of a mixture of carbon mon- 
oxide and nitrogen, having 
exactly the composition of 
simple producer-gas. In addition there will be a small 
quantity of hydrogen from the moisture contained in the air. 
These gases will be powerfully reducing, and therefore the 
atmosphere in a blast-furnace will be always reducing, and 
the oxide of iron or other metal charged into the furnace 
will be reduced by the carbon monoxide, thus adding carbon 
dioxide to the gases ; and as this reaction takes place at a 
moderate temperature, the reduction will be largely if not 
completely effected near the top of the furnace. Sulphides 
are not acted on by carbon monoxide or carbon, so that in 




Fig. 56. — Typical Blast-furnace. 
Shaft. B, Bosh. H, Hearth. TA, Tuyere 
opening, bm, Blast main, cg, Charging 
gallery. GM, Gas main. DB, Dust box. 
GP, Waste-gas pipe. 



218 FUEL 

the absence of special reducing fluxes sulphide ores are melted 
but not reduced in the blast-furnace. 

The satisfactory working of a blast-furnace depends on 
several conditions, among which the regular ascent of the 
gases, the regular descent of the charge, and the proper cool- 
ing of the gases are of the utmost importance. The first two 
depend very much on the form of the furnace ; and it is only 
by long experience that the forms now in use have been 
evolved. In the best modern furnaces, if the greatest 
diameter be taken as 1, the height will be 3-5, the width at 
the stock-line, i.e. at the top of the charge when the furnace 
is full, -75, and the hearth about -4 ; so that for an 80-foot 
furnace the dimensions would be : Height = 80 feet, diameter 
at bosh 23 feet, diameter at stock-line 17 feet, diameter of 
hearth 9 feet or thereabouts, and the angle of the bosh 
should be about 75°. 

The proper cooling of the gases necessitates a sufficiently 
high column of material in the furnace to absorb the sensible 
heat of the gases as they rise. The hearth and boshes of 
the furnace are subjected to very great heat, and therefore 
must be built of very refractory materials ; and in order 
to prevent them being rapidly cut away, water-blocks, i.e. 
iron blocks through which water can be made to circulate, 
are very frequently built into the masonry of the bosh. 

The blast-furnace is a very economical machine, in spite 
of the fact that the carbon is only burnt to carbon monoxide, 
and therefore only evolves about one-third the heat which 
it is capable of giving on complete combustion ; but as the 
gases given off are combustible the remainder of the heat can 
be obtained by burning them. 

Either charcoal, coke, or coal may be used in the blast- 
furnace under certain conditions, and the size and method of 
working to a very large extent depends on the nature of the 
fuel. The furnace must not be so high that the weight of 
the superincumbent charge will crush the fuel, or the blast 
will be impeded, and the working of the furnace therefore 
interfered with. 



FUKNACES FOR METALLURGICAL PURPOSES 219 

For charcoal, about 30 or 40 feet seems to be the greatest 
satisfactory height ; for coke, the furnace may probably be any 
height that other conditions allow, if the coke be of first-class 
quality, but if it be of inferior quality the advantageous 
height will be much limited. In the case of certain American 
cokes the height of charge which would crush the coke was 
found to vary from 70 feet as a minimum to 128 as a maxi- 
mum. The highest furnace in use using Durham coke in the 
Cleveland district is 101 feet, and this is found to be rather 
too high for satisfactory working. 

Only certain qualities of coal are suitable % for blast-furnace 
use. A strongly coking coal which softens and fuses is not 
satisfactory, as it impedes the blast ; it is only the less strongly 
coking varieties, therefore, that are available, either the an- 
thracitic or splint varieties. In America anthracite has been 
used, but its great density and lack of porosity renders it 
somewhat unsuited for blast-furnace work. The splint coals 
used in Scotland are quite suitable, but they yield compara- 
tively little coke, and as this coke is soft and friable high 
furnaces cannot be used, so that about 60 feet is found to be 
the maximum height that is advantageous. 

In the selection of a fuel for blast-furnace use it must be 
remembered that it is only the fixed carbon that is of any use 
for producing heat in the furnace, all volatile matter being 
expelled before the fuel reaches the zone of combustion, so 
that in estimating the fuel value of a coal for this purpose no 
notice must be taken of the portion which is volatile. As the 
splint coals of Scotland only yield about 50 per cent of coke, 
their value is little more than half that of a coke. 

In selecting a coke for furnace use attention must be paid 
to its actual heating power and to its physical condition, 
especially its crushing strength, and in selecting a coal atten- 
tion must be paid to its coking properties, and to the amount 
and nature of the coke which it produces. 

A very important property of coke, on which much of its 
value for blast-furnace use depends, is its power of resisting 
the action of carbon dioxide. By the changes which take 



220 



FUEL 



place at the top of the furnace — reduction of oxide of iron 
and decomposition of limestone — carbon dioxide is added to 
the gases. Under suitable conditions this attacks carbon and 
forms carbon monoxide, C0 2 + C=2CO, thus consuming 
more coke without doing any good. The temperature at 
which this action takes place varies with different forms of 
coke, and obviously the less readily it takes place the more 
efficient, other things being equal, will the coke be. 

The following table of the properties of some American 
cokes will illustrate the variations which may take place : * 



Locality. 


Pounds in One 
Cubic Foot. 


Percentage. 


111 

ail 


Height of Charge 

which it will 

support without 

crushing. 


m 

OB 

S 

a 
•a 
3 

W 

3-50 
3-15 
3-35 
3-60 
3-00 
3-50 
3-20 


o 

Pi 


Dry. 


Wet. 


Coke. 


Cells. 


Connelsville 
W. Virginia 
Broad Top . 
Clearfield . 
Cumberland 
Alabama . 
Illinois 


47-47 
52-54 
44-81 
56-35 
48-61 
50-70 
4202 


7715 

81-56 
76-88 
76-69 
82-41 
69-01 
6509 


61-53 
64-33 

58-27 
74-43 
58-96 
73-77 
63-79 


38-47 
35-67 
41-73 
25-57 
41-04 
26-23 
36-21 


284 

258, 

240 

319 

215 

225 

180 


114 

103 

96 

128 
86 
87 
70 


1-500 

1-342 

1-56 

1-750 

1-493 

1-215 



Sir I. Lowthian Bell, in some experiments on cokes made 
in the beehive and in the Simon-Carves oven, found that 
though the two cokes differed very slightly in calorific power, 
the ratio being 100 : 98*5, the amount required in the blast- 
furnace to do equal work was in the ratio 100 : 91 ; and on 
examining the gases from the furnaces he found that those 
from the former contained a considerably larger quantity of 
carbon dioxide than those from the latter. From examina- 
tion in the laboratory it was found that the one form of coke 
was more readily attacked by carbon dioxide than the other. 

Another important property is the cell structure of the 
coke. The calorific energy of a blast-furnace depends on the 
amount of surface which is exposed to the oxygen of the air, 



1 Fulton, Transactions American Institution of Mining Engineers, 
vol. xii. pp. 212-223. 



FURNACES FOR METALLURGICAL PURPOSES 221 

in the region of the tuyeres, and this depends on the amount 
of cell space ; for this reason, charcoal, which is much more 
cellular, is more efficient fuel than coke. 

The following table, by Sir I. Lowthian Bell, 1 will give an 
idea of the actual efficiency of an iron-smelting blast-furnace. 
The figures are for each 20 lb. of iron produced : 

Centigrade units. B.Th.U. 



Evaporation of water in coke 


313 


563 


Reduction of oxide of iron . 


33108 


59595 


Carbon impregnation .... 


1440 


2592 


Expulsion of C0 2 from limestone. 


4070 


7326 


Decomposition of C0 2 from limestone . 


4224 


7603 


Decomposition of water in blast . 


1700 


3060 


Reduction of phosphoric acid, sulphuric aci 


'\ 3500 


6300 


and silica ..... 






Fusion of pig-iron .... 


6600 


11880 


Fusion of slag ..... 


15356 
70311 


27641 


Heat usefully employed 


126560 


Carried off in gases .... 


7900 


14220 


Otherwise lost ..... 


8789 


15820 


Total 


87000 


156600 



giving an efficiency of about 80 per cent of the heat evolved 
by the fuel consumed, only about 9 per cent being carried off 
as sensible heat in the gases. 

The amount of fuel actually consumed in smelting iron 
ores is about 18 to 21 cwt. of coke, or 30 to 36 cwt. of 
coal per ton of iron produced. 

The smelting of ores of lead and copper in the blast- 
furnace was for a long time unsuccessful, as the metallic 
oxides very rapidly corroded the brickwork. This difficulty 
has now been overcome by the introduction of the water- 
jacket. This is a casing of either wrought or cast iron, 
through which water is made to circulate. This has the 
effect of cooling the charge, so that the interior becomes 
covered with a layer of slag which is being constantly 
formed and melted away. The circulation of the water 
carries away some heat, and this reduces the actual efficiency 

J Principles of the Manufacture of Iron and. Steel, p, 95. 



222 



FUEL 



of the furnace, but it has rendered the furnace available for 
purposes for which it could not be used before. 

Most of the water- jacketed furnaces used for lead smelting 
in America are rectangular in form instead of circular. 

The Hot Blast — 
The hot blast was in- 
vented by Neilson in 
1828, and very rapidly 
came into general use, 
as it led to very great 
economy in the use of 
fuel. The amount of 
heat developed in the 
furnace is far less with 
the hot blast than with 
the cold. The saving 
is due to the fact that 
much less air is passed 
through the furnace, 
and therefore there is 
ess heat carried away 
by the waste gases ; 
and also that the air 
being hot, there is less 
expansion to take place 
opposite the tuyeres, 
and as expansion ab- 
sorbs heat there is thus 
less cooling. As the hot 
blast is only of practical 
importance in the smelting of iron, it will be fully described 
in the volume on iron. 

Hearths. — The hearth resembles the blast-furnace in the 
fact that the fuel and the substance to be heated are in con- 
tact, but it differs in almost every other respect. 

It is usually a shallow chamber or vessel, in which the 
charge is placed. The air is supplied by means of tuyeres, 




Fig. 57. — Blast-furnace for smelting Lead. From 
Hoff man's Lead, o, Tuyeres. F, Water-jacket. 
d, Siphon tap. r, Blast main. 



FURNACES FOR METALLURGICAL PURPOSES 223 

and is either directed downwards on to the surface of the 
charge or horizontally just below the charge. 

The combustion is usually more complete than in the 
blast-furnace, the carbon being to a large extent burnt to 
carbon dioxide, but the escaping gases usually contain con- 
siderable quantities of unconsumed combustible gases. 
Owing to the way in which the air is supplied, the atmosphere 
is not so powerfully reducing as that of the blast-furnace ; 




C, The hearth. 



Fig. 58.— Refinery Hearth. 
E E, Hollow water-jacketed walls. T T, Blast-pipes, b b, Tuyeres. 



it may be actually oxidizing. The hearth, therefore, can be 
used for various operations : direct reduction, as in the 
Catalan forge ; oxidation, as in the Yorkshire finery ; or 
combined oxidation and reduction, as in the Scotch ore- 
hearth. The amount of fuel consumed is not large, and on 
the whole the hearth is a fairly economical furnace for those 
operations for which it is suited. It has the advantage also 
of being cheap and easy to erect, and it is therefore largely 
used in new districts or where labour and material are 
expensive. 



224 



FUEL 



The Reverberatory Furnace. — This furnace is entirely 
different in principle from those already described, the fuel 
not being in contact with the material that is heated. The 
fuel is burned on a separate grate, whilst the material to be 
heated is in a separate chamber, the hearth, into which the 
products of combustion pass. Between the grate and the 
hearth is a ridge of brickwork, the fire-bridge, and between 
the hearth and the chimney there is often another ridge, the 
flue-bridge, over which the products of combustion pass. 

The whole furnace is covered with an arched roof, which 
is usually highest over the fireplace and slopes down towards 
the flue, so that the flame may be reverberated or reflected 

downwards on to the 
hearth, whence the 
name reverberatory 
furnace. The roof 
is usually a very flat 
arch springing from 
the side walls of the 
furnace. As the 
weight of this arch 

FIG. 59. — Reverberatory Furnace for calcining Copper Ores, exerts a Considerable 
H H, Hearth. F, Fireplace. B B, Hoppers. 

outward thrust, the 
walls of the furnace must be securely tied. Usually the 
side walls are cased with iron plates, and strong vertical 
rods are fixed into the ground at each side and are tied 
by cramps into the masonry, and are held together at 
the top by strong stays passing across above the furnace 
roof. The vertical or buck stays may be of any form, 
but are preferably of T section, the projecting limb not 
extending quite to the top, and a hole being made at 
the top through which the head of the cross stay can pass. 
Where economy is an object old rails make excellent buck 
stays. The cross stays are circular or square in section, and 
in the case of the first-named kind, they are held by a head at 
one end and a screwed nut at the other. When rails or similar 
buck stays are used the cross stays are provided with eyes 




FURNACES FOR METALLURGICAL PURPOSES 225 

which pass over the top of the vertical stay and are wedged 
into position. The cross ties must not be fixed rigidly, but 
must be capable of adjustment, for as the furnace gets hot 
the masonry of the arch will expand, and unless provision 
be made to allow for this the crown of the arch may be 
thrown up and broken. 

The hearth itself is usually carried on an arch of brick- 
work, so that there is a vault or chamber under the furnace 
to which access can be obtained when necessary. The 
furnace will usually be provided with a series of working 
doors, one, two, or three at each side, and sometimes one at 
the end, in which case the flue is taken off at the side ; all 
the doors are fitted into cast-iron frames securely built into 
the masonry. The doors themselves are iron or fire-brick 
plates, which are lifted up and down as required, and are 
luted air-tight with clay when necessary. The charge may 
be introduced through the side doors, or through a hole in 
the roof, which is usually provided with a hopper. 

Reverberatory furnaces are in general used for two 
purposes, for roasting and fusion with or without reduction, 
and the form and size of the hearth will depend on the pro- 
cess for which it is to be used. 

For roasting furnaces the hearth is usually flat, made of 
fire-brick slabs carefully set in clay. The sills of the work- 
ing doors are either level with the hearth, so that the charge 
can be raked out on to the floor, or if they are higher, openings 
are provided under each, by which the charge can be raked 
into the arched chamber beneath the furnace. This is 
always advisable when the roasted charge is likely to give off 
noxious fumes as it cools. In some cases iron receptacles 
for the charge are provided outside the furnace under the 
doors into which the charge can be drawn, and the escaping 
gases pass into the furnace by the doors and thus to the 
chimney. 

The hearth may be rectangular or oval in form. It must 
not be so long that it cannot be uniformly heated — 16 feet 
may be taken as being about the maximum length ; and as 

(D107) q 



226 FUEL 

the charge will have to be turned by the workmen, it must 
not be so wide that the rabbles have to be inconveniently 
long — about 10 feet is the maximum allowable width. It 
must be so shaped that every portion of it can be reached 
by means of a rabble or rake from the working doors, and 
therefore sharp corners are usually filled up with masonry, 
and in the spaces between the doors wedges of masonry are 
built. It sometimes happens, in cases where only a very 
moderate temperature is required, that the part of the charge 
nearest the fire-bridge may become overheated, and to pre- 
vent this a false or curtain arch may be built from the fire- 
bridge to about one-third the length of the hearth. As a 
copious supply of air is needed for roasting, various air- 
openings are often left through the side wall, or through the 
bridge, which is then called a " split bridge." 

For roasting, furnaces with more than one hearth are 
often used. In this case two or more hearths are placed end 
to end, each being about three inches higher than the one 
behind, and each being provided with its own working doors. 
The charge is let down on the hearth farthest from the fire- 
place, and is moved forward and ultimately drawn from the 
hearth nearest the fire, so that there will always be, in a 
three-hearth furnace, three charges being treated at once. 
Two -hearth furnaces are often advantageous, three-hearth 
are sometimes useful, but furnaces with more than three 
hearths are very rarely satisfactory, and can only be used 
in cases where the material under treatment contains 
enough sulphur to evolve a considerable amount of heat 
on oxidation. 

When the furnace is to be used for fusion, the arrange- 
ment is somewhat different. The hearth is smaller, may or 
may not be provided with working doors at the side or end, 
and instead of being flat it is made curved, so that melted 
material will all flow towards the lowest point — the well, 
where it will collect till it is tapped out by means of the tap- 
hole, or, as in the case of copper refining, ladled out into a 
metal pot or moulds. The form of the hearth is usually 



FURNACES FOR METALLURGICAL PURPOSES 227 



roughly given by bricks built in steps, and on this is laid the 
working bottom of slag or some other material not likely to 
be acted on by the charge. In many cases, where a very 
high temperature is required, the hearth is carried on iron 
plates so arranged that air can circulate quite freely under 
it, or in others the hearth may be merely an iron pan, lined 
or not with refractory material. 

The fireplace is usually fed from the side. It should not 
be more than about 6 feet deep from the door, or it will be 
impossible to distribute the fuel evenly by hand. The ratio 
of the size of the fireplace to that of the hearth varies very 
much, and depends on the temperature which it is required 
to attain, and also on the nature of the fuel. It is largest in 
the case of the puddling furnace, a furnace with a very small 
hearth, and in which a very high temperature is required, 
and it is smallest in roasting furnaces, where it is often not 
more than one-twentieth, and between these there is every 
possible variation. The following table gives the details of 
a few typical furnaces : 





S3 

a 

3 


" O 
6C 3 


u 

<D 

Pi 

a 
o 
ox. 

>-*- 05 


o 
eg 

a . 


§ 

sS 

1. 

N;3 


3 

a . 


5 
"3 

<n . 


60 

.9 
'3 . 

©T5 
« g 




be 
•S 
2 


.3° 


J3 


So 


-2 




Pi 


Piw 
Pi 




TJ 


S a 


*eS 


2 


a 


3 


o 


O 




s 


<3g 


o 


s 


— 


o 


o 


O 




Ph 


p^e 






fe 








Fireplace — 


















Length 


3-5 


4-3 


30 


40 


2-5 


1-9 


3-5 


3-75 


Breadth . 


2-5 


5-5 


50 


40 


40 


20 


40 


4-5 


Area . 


8-75 


23-65 


150 


160 


160 


3-8 


140 


16-9 


Hearth — 


















Length 


60 


150 


190 


130 


110 


2-5 


140 


13-5 


Breadth . 


3-75 


5-5 


110 


90 


100 


40 


9-5 


90 


Area (approxi- 


















mate) 


200 


750 


2000 


1120 


104-0 


100 


12-6 


1170 


Ratio-area of fire- 


















place to area of 
hearth(approxi- 


































mate) 


1:2-3 


1 : 3-2 


1 : 130 


1:7-0 


1 : 10-4 


1:3 


1:9 


1:7 


Height of arch 


















above bridge . 


10 


3-9 


1-5 


1-67 


•8 


•8 






Depth of fireplace 


















below bridge . 


1-5 


•8 


2-0 


30 


2-0 


1-4 







The height of the bridge above the hearth is about 1 foot 
to 1 foot 9 inches, and all details may vary very much, 



228 FUEL 

according to the purpose for which the furnace is to be used, 
and the taste of the builder. 

The arrangement of the fireplace will vary with the nature 
of the fuel and the temperature which it is required to 
attain. The area of the fireplace includes both that of the 
fire-bars and the spaces between them. The width of the 
space between the bars is determined by the nature of the 
fuel, that of the bars is limited by the need for making them 
sufficiently large to be durable and to resist warping. The 
fire-bars will usually be | inch or more in thickness. They 
are made of cast-iron, and are cast with square lugs at each 
end, which fit together when the bars are in position and 
thus regulate the distance between them, or they may consist 
of 1J to lj inch square bars of iron resting on bearers. The 
bars should be cast from grey pig-iron with the addition of 
scrap, and should not exceed 40 inches in length. The bars 
are almost always placed horizontally, but they may be 
slightly inclined backwards. For large coal the space 
between the bars may be up to § inch, but with smaller coal 
the spaces must be much less. In the case of anthracite 
coal, if the bars were placed close enough to prevent 
great loss by falling through, the draught would be 
unduly impeded, and to prevent this, in South Wales, 
where such coals are used, a deep layer of clinker is 
allowed to accumulate on the bars, which acts as a grate, 
and which also serves to heat bhe air as it rises, the 
clinker being from time to time broken up and removed 
through the bars, so as to maintain the bed at a convenient 
thickness. 

The amount of fuel which can be burned on the hearth of 
a reverberatory furnace depends firstly on the nature of the 
coal, and secondly on the air supply. The more air, of 
course, the more rapid will be the combustion. 

The more caking the coal, the less of it can be burned on 
a given grate area. " Of very caking coals not more than 
12 to 14 lb. per square foot per hour should be burnt ; if 
less caking, from 14 to 16 lb. ; and if non-bituminous, from 



FURNACES FOR METALLURGICAL PURPOSES 229 



16 to 20 lb. may be used." 
bustion in various grates : 



Rankine gives the rate of com- 



1. Slowest rate of combustion in Cornish boilers 

2. Ordinary rate in these boilers . 

3. Ordinary rate in factory boilers . 

4. Ordinary rate in marine boilers .... 

5. Quickest rate of complete combustion, the supply 

of air coming through the grate only 

6. Quickest rate of complete combustion of caking 

coal, with air-holes above the fuel to the extent 



Lb. per Sq. Ft. 
per Hour. 

4 



12 to 
16 to 



10 
16 
24 



20 to 23 



of one-thirtieth the area of the grate 




34 to 27 


7. Locomotives . . . . . . . 40 to 120 


Gruner gives — 


Lb. per Sq. Ft. 


per Hour. 


1. Furnace for roasting sulphides . . 3 to 8 


2. Fires for stationary boilers 








8 to 20 


3. Furnaces used in smelting lead 








12 to 16 


4. Furnaces for copper smelting 








15 to 30 


5. Puddling furnaces 








20 to 30 


6. Steel-melting furnaces 








41 to 81 


7. Locomotive fires 








81 to 102 



The thickness of the layer of fuel is also important. The 
thinner the layer of fuel, the better will be the draught, and 
the more coal can be burned ; but if it be too thin, air may 
get through unconsumed, and thus the efficiency will be 
seriously reduced. " The limits of thickness over the grate 
are 1 \ to 5 inches for bituminous coal, and 1 \ to 8 inches for 
brown coal. Peat, which is not pulverized by fire, may be 
piled as high as the space around it will allow." x 

One advantage of the reverberatory furnace is that the 
atmosphere can be regulated so as to fit it for various pur- 
poses. If a large excess of air be admitted above the fuel, 
combustion will be complete, and the atmosphere will be 
powerfully oxidizing ; if, on the other hand, the amount of 
air be restricted, the combustion will be less complete, carbon 
monoxide and other reducing gases will be present, and the 
atmosphere will be powerfully reducing. 

It will be seen that the heating in a reverberatory furnace 

1 Schmackhofer and Browne, Fuel and Water, p. 96. 



230 



FUEL 



is entirely produced by the flame of the fuel and the heat of 
the products of combustion. A flame could be obtained by 
burning coke on the hearth in sufficient thickness to ensure 
the production of a large quantity of carbon monoxide ; but 
such a flame, being non-luminous, would have little radiative 
power, and therefore would be very inefficient. The coal 
used should be moderately caking, and should yield a con- 
siderable quantity of gas on distillation, so as to produce a 
large bright flame. 

The reverberatory furnace is not by any means an eco- 
nomical form of apparatus, the losses of heat being always 
very high. Griiner states that the efficiency of a reverbera- 
tory furnace melting pig-iron is only 8-5 per cent ; but Major 
Cubillo has recently pointed out that this estimate is too 
low, the data not having been accurate. Taking the puddling 
furnace as the type of a reverberatory furnace, Major Cubillo 
obtains in a special case the following results, which he states 
in the form of a balance-sheet : 1 



General Balance of the Reverberatory Furnace. 



Heat produced. 


Heat consumed. 




Calories. 


Per 

Cent. 




Calories. 


Per 

Cent. 


Heat of fuel . 

Heat of substances 

oxidized during the 

process 


163960 
3106 


98-12 

1-88 


Fusion of the iron 
Fusion of the slags . 
Vaporization of water 

in the fuel 
Heat carried off by 

gases .... 
Heat lost in ashes 
Loss by radiation, etc. 


26210 
2246 

2133 

128900 
1990 
5618 


15-60 
1-34 

1-27 

7713 
113 

3-35 


167066 


10000 


167097 


99-82 



The efficiency being therefore 16*94 per cent. In most 
cases of reverberatory -furnace work the efficiency is far less 
than this, the loss by radiation being usually very much 
higher. 

Major Cubillo 2 has worked out the thermal values of 

1 Proc. S. Staff. Institute of Iron and Steel Works Managers, 1893- 
1894, p 13. 

2 J. I. and S. I., 1892, vol. i. pp. 245 et seq. 



FURNACES FOR METALLURGICAL PURPOSES 231 



the changes on a gas-fired puddling furnace, with a view 
of ascertaining its efficiency. The details cannot be 
understood without a consideration of the chemistry of 
the process, as heat is obtained not only from the fuel 
but also by the reaction in the furnace. A summary of 
the results may be of value. The heat received is thus 
summed up : 





Calories. 


Per Cent. 


Heat brought in by producer-gas . 
Combustion of 135-73 CO and 6-72 H x 






197-8 
5210 


22-70 
59-80 


Heat introduced by air . 






86-7 


9-96 


Oxidation of silicon . 














26-1 


2-90 


„ manganese 
„ carbon . 














2-0 

29-8 


•22 
3-45 


„ phosphorus 
„ sulphur 
„ iron 














•2 
•2 

6-3 


•02 
•02 

•72 




870-1 


99-79 



Heat consumed : 





Calories. 


Per Cent. 


Latent heat of fusion 


5-2 ) 


2-90 


Heat of blooms .... 










20-1 1 


Heat of fusion of cinder . 










231 


2-64 


Vaporization of water in ore 










5-4 


•60 


Lost up stack .... 










366-7 


42-14 


Vaporization of water in gas . 










7-6 


•87 


Reduction of Fe 2 3 to FeO . 










14-1 


1-61 


Reduction of Mn 2 3 to MnO . 










3-3 


•38 


Heat of ash .... 










9-6 


Ml 


Radiation 










415-0 


47-70 




870-1 


99-95 



These figures, of course, refer only to the one charge with 
which the experiment was made in the arsenal at Trubia ; 
but probably others would not be far different. The effi- 
ciency as shown by the figures is only 2*9 per cent. It would 
be much larger probably with furnaces of larger size, the 



Per 100 kilogrammes of blooms. 



232 



FUEL 



extreme shortness of the puddling furnace being very favour- 
able to loss of heat in the gases. 

The reverberatory furnace may be modified in various 
ways for various purposes. The hearth may be made 
circular and may be made to rotate horizontally, or the 



WL 




Fig. 60.— The Stetefeldt Furnace. 

whole working space may be made cylindrical and may be 
made to rotate vertically. These devices are to ensure 
constant stirring of the charge, and do not in any way alter 
the principles on which the furnace is based. When wood 
is the fuel used, the fireplace is frequently made with a solid 
bottom, as air can find its way quite readily enough into a 
mass of wood without the use of fire-bars. 



FURNACES FOR METALLURGICAL PURPOSES 233 



The draught is usually produced by means of a chimney, 
but artificial draught may be used. If the ash-pit be closed 
air-tight a blast can be sent in beneath the bars, and another 
supply of air may be sent in above the fuel, in order to ensure 
complete combustion of the products of distillation. 

Another type of furnace, the Stetefeldt furnace, which is 
usually used for the chloridizing roasting of silver ores, be 
longs to this group. The ores are sulphides, and therefore no 
additional fuel is required, and the roasting takes place whilst 
the powdered mineral, 
mixed with salt, is fall- 
ing down a vertical shaft 
which is kept hot by 
fireplaces g near the 
bottom ; the roasted ore 
falls into a hopper and is 
withdrawn. The size of 
these furnaces varies ; 
they may be up to 35 
or 40 feet high and 5 
feet square, and will 
treat from 40 to 50 tons 
of ore per day. Some of 
the most recent Stete- 
feldt furnaces are fired 
with gas. 

Crucible Furnaces. — These furnaces are of many kinds. 
The usual crucible furnace, such as is used for assaying pur- 
poses, for making alloys, and in the manufacture of crucible 
cast-steel, is a rectangular or elliptical chamber, provided at 
the bottom with fire-bars and at the top with a cover, whilst 
a flue in one side near the top serves to carry off the products 
of combustion. The crucible is placed in a furnace resting 
either on the fuel or on a brick placed on the fire-bars. The 
fuel used is coke or anthracite — generally the former. The 
combustion is imperfect, carbon monoxide only being formed, 
and owing to the small quantities of material which can be 




Fig. 61. — Crucible Furnace. 



234 



FUEL 



treated at once such furnaces are very wasteful of fuel. 
Crucible furnaces may be worked either with or without blast. 
With a blast a very high temperature can be attained. A 
very good example of a crucible furnace with a blast is Messrs. 
Morgan's Annular Hot-air Furnace (Fletcher's patent). In 
this the fuel rests on a solid dished bottom, into which the 
air is supplied, the crucible to be heated being placed on a 
stand in the centre of the furnace. This furnace gives a very 
high temperature, and acts very quickly, thus leading to 

considerable saving in 
fuel. 

One objection to the 
use of crucibles is that 
in order to pour their 
contents they must be 
lifted into the air. This 
not only cools them, 
thus causing loss of 
heat, but also often 
causes the crucible to 
crack. This difficulty 
is overcome in the 

Fig. 62.— Fletcher's Patent Furnace. , , 

A, Air tube, i, Iron casing of furnace. F, Fire-brick Morgan S Tilting 1 Ur- 
lining. B,Flue. c, Cover with fire-brick lining D. nace The furnace fe 

an octagonal steel shell, cased with fire-brick ; it is provided 
with a grate, and stands over an air-chamber from which 
air is supplied under pressure. The crucible is fixed by 
means of blocks into the casing, and the casing is so fixed 
that it can be rotated in such a way that the spout is the 
centre of rotation. When the charge is to be poured, the 
blast is turned off, the chimney disconnected, the furnace 
body turned by means of a screw gear, and the molten metal 
poured out of the spout into the moulds. In another form 
of the furnace the body is carried on trunnions, and is so 
arranged that it can be lifted away bodily by means of a 
crane and carried to the moulds. 

Muffle Furnaces. — In this type of furnace a separate 




FURNACES FOR METALLURGICAL PURPOSES 235 



large vessel is heated by means of a fire. The fire is usually 
placed underneath, or at one end of the muffle, and the pro- 
ducts of combustion are made to circulate both above and 
below. Such furnaces are only used when either the sub- 



L, Ash-pit. K, Man-hole. 
M, Air main with valve N. 
I, O, Annular air ring. H, Per- 
forated base of furnace. E, 
Support for crucible. P, 
Chimney. c, Cover with 
fire-brick lining R. A, Iron 
ring to which are attached 
the pins by which the casing 
is lifted. P, Detachable 
chimney. F, Spout. 




Fig. 63.— Piafs Oscillating Furnace. 

stance being heated would be injured by contact with the 
gases, or where products are evolved which it is required to 
keep free from mixture with the products of combustion. 
Furnaces of this type are usually called close roasters. They 
are essentially reverberatory furnaces ; but the charge is 




1 






■//,?/)//////)/)/////////?//////)/)////////77. 







Fig. 64. — Muffle Furnace. 



heated not by contact with or radiation from the flame, but 
by radiation from the hot walls of the muffle. 

Retort Furnaces. — The only peculiarity of these fur- 
naces is that all or part of the charge is volatilized and has to 
be condensed. They may be either of the type of muffle or 
crucible furnaces. Where there is a liquid residue which has 
to be poured out, furnaces of the crucible-furnace type are 
often used, and the body of the retort is lifted out after each 



236 



FUEL 



charge, or to avoid this, tilting furnaces are sometimes 
used. 

Boiler Furnaces. — Fuel is very largely used for steam 
raising, and the feeding of boiler furnaces is a matter of 

extreme importance. If 
the boilers are badly fired 
the fuel is very wastef ully 
used, and a large quantity 
of smoke is often pro- 
duced. 

The fuel is supplied 
to a fire grate, and the air 
may be supplied either 
by chimney draught or 
under pressure. The 
chief air supply is always 
below the bars, but an 
additional air supply is 
sometimes arranged 
above the bars. If smoke 
is to be prevented it is 
essential that air be sup- 
plied in such a way that 
it will mix with the 
hydrocarbon gases before 
their temperature has 
fallen below ignition 
point, and thus complete 
the combustion. 

Ordinary hand firing 
is as a rule very unsatis- 
factory. The coal is supplied in comparatively large portions 
at a time, and the conditions are much the same as those 
already described for a domestic fire. When the doors are 
open for firing, cold air rushes in and cools the gases, and 
very often every time coal is added dense black smoke escapes 
from the chimney. It is almost impossible to make hand 




Fig. 65. — Retort Furnace for distilling Zinc. 

c, Fireplace. G, Ash-pit. B, Air passages. 

T, Chimney. 



FURNACES FOR METALLURGICAL PURPOSES 237 

firing satisfactory, but the smaller the quantity of fuel added 
at a time the better it will be. 

To overcome the difficulties of hand firing, mechanical 
stokers, in which the fuel is added continuously or in small 
portions at a time, are now largely used. These are of two 
kinds. 

Coking Stokers. — As an example of this type Messrs. 
Meldrum's " Koker " Stoker may be taken. The principle of 
all the coking stokers is that the fuel is fed on to a " dead " 
plate, i.e. a plate through which air cannot pass ; there it is 
coked by the heat of the furnace, and the volatile products 
of distillation pass over the hot burning fuel, and are raised 
to a high temperature and burnt. 

In the Meldrum furnace the coal is supplied to a hopper in 
front of the furnace, and beneath this is an oscillating cast- 
ing b, which rocks backwards and forwards. When it comes 
under the hopper it is rilled with coal, and as it rocks forwards 
it empties its contents on to the coking plate d, whence it is 
pushed forward at each oscillation of the rocker. By the 
time it has reached the end of the coking plate, the volatile 
matter has been expelled, and the coke is pushed on to the 
bars. The fire-bars are corrugated and are moved backwards 
and forwards by means of a cam. They all move forward 
together, and so carry the coke forward, but are drawn back 
singly, so as not to take it back with them. In some cases 
perforated coking plate is used, and air is supplied just above 
it. Forced draught may be used. 

The combustion is very rapid and very complete and is 
almost smokeless. 

Closely allied to the coker stokers are the chain-grate 
stokers, in which the solid bars are replaced by chains which 
are moved slowly forward, carrying with them the fuel, so 
that the fuel is always received at the end farthest from the 
flue and is there distilled. 

Sprinkling Stokers. — In these stokers the fuel is 
sprinkled in small quantities at a time on the surface of the 
fuel, the action thus resembling in some respects good hand 



238 FUEL 

firing, but differing from it in that the additions are very 




frequent and very small, and that the fire doors are not 



FURNACES FOR METALLURGICAL PURPOSES 239 
opened. As an example the Proctor Stoker may be taken. 




The fuel is fed into a hopper, from which it falls into an iron 
box, fitted with a ram which moves backwards and forwards, 



240 



FUEL 



As it goes backwards coal falls into the box, as it goes for- 
ward it pushes the coal into the sprinkler box. The shovel 
is drawn back by a cam, and as it recedes the coal falls 
in front of it. As soon as it reaches the back of the box it 
is released and is brought rapidly forward by the spring h, 
so that the coal is shot out into the fire, this action being 
repeated at any required speed. 

The bars are supported on bearers, the bearer farthest 
from the fire door being kept cool by the circulation of steam, 
and each alternate bar is made to reciprocate so as to break 




Fig. 68.— Mond's Gas-fire. 



up the clinker and ultimately deliver it over the ends of the 
bars to the ash-pit. 

Underfeed Stokers. — These stokers are of recent origin 
and have been designed to work with a thick bed of fuel, the 
feed being obtained by Archimedean screw or chain grate. 
Fuels having a low percentage of volatile matter, such as 
anthracite and coke breeze, and others of as high ash content 
as 50 per cent, can be burned with advantage over other 
types of stokers. 

Almost all automatic stokers must be fed with slack or 
coarsely powdered fuel, and they all use some steam to drive 
the necessary mechanism. 

Furnaces for Gaseous Fuel. — Many forms of furnace 
for the use of gaseous fuel have been suggested, the simplest 
of which are but slight modifications of a reverberatory 



FURNACES FOR METALLURGICAL PURPOSES 241 

furnace. In fact, if the fireplace of a reverberatory furnace 
be made very deep, and be worked with a thick layer of fuel, 
it becomes a gas producer, as is seen in the Mond gas-fire. 

Boetius Furnace. — This furnace was patented in 1865. 
It is an ordinary reverberatory furnace to which a gas pro- 
ducer is attached, but the side walls and roof are provided 
with passages through which the air can circulate so as to 



SECTION ON LINE A.B. 




FIG. 69. — Boetius Heating Furnace. From D. K. Clark's Fuel. 

become heated before passing to the furnace, where it mixes 
with the combustible gases just as they enter. 

The Becheroux Furnace. — This is a modification of 
the Boetius furnace, in which the proportion of the parts is 
different and a mixing chamber is provided for the air and 
gases before entering the furnace proper. 

Furnaces fired in this way have not proved a great success 
owing to the low calorific power of the gas. Attempts have 



(D107) 



B 



242 FUEL 

also been made with more or less success to work kilns by 
means of gas, the gas and air being admitted by two series of 
openings, one above the other. 

Gas furnaces did not become a practical success till 
Siemens introduced his regenerative furnace. The principle 
of the regenerative furnace is very simple. Each furnace is 
provided with four chambers or regenerators, placed in any 
convenient position, and filled with a chequer-work of fire- 
brick. The air and gas are supplied at one end of the furnace, 
burn, and the products of combustion pass away at the other 
end to the chimney through one pair of regenerators. When 
these regenerators are hot the direction of the current is 
reversed, the air and gas are sent through the hot regenerators 
and thus reach the furnace at a high temperature, whilst the 
products of combustion pass away through the other re- 
generators. The direction is reversed every hour or half- 
hour, so that the regenerators are kept very hot, and whilst 
two are always being heated the other two are heating the 
air and gas. 

Such a furnace consists of three essential parts — (1) the 
gas producer, (2) the furnace proper, (3) the regenerators with 
the necessary valves. 

The gas producers have already been described. The 
furnace is simply a reverberatory furnace, but in place of a 
fireplace it is provided at each end with gas and air ports, 
which may open directly into the furnace or into a mixing 
chamber. The roof must be built of very refractory bricks, 
silica bricks being commonly used, whilst the hearth will 
either be of sand, dolomite, or other material according to the 
purpose for which the furnace is to be used. The whole 
furnace is preferably cased with iron and must be securely 
stayed. The gas and air are supplied from ports — rectangular 
openings at each end, the number varying, but always being 
odd — placed so as to break joint. The gas ports are below 
and the air ports above, so that the heavy air tending to 
descend and the lighter gas tending to ascend, the mixture 
shall be complete. The roof in the furnaces designed by 



FURNACES FOR METALLURGICAL PURPOSES 243 



Siemens was depressed towards the middle of the furnace, so 
as to deflect the flame down on to the charge on the hearth. 







The regenerators were placed underneath the furnace by 
Siemens, and have generally been built in the same position 
since. The four chambers may be all of one size, but usually 



244 FUEL 

the air regenerator is from 20 per cent to 40 per cent larger 
than the gas regenerator. The regenerators are filled up 
with refractory brickwork, set chequerwise, so as to allow 
free passages for the gas, and at the same time to ensure 
sufficient contact for thorough heating or cooling as the case 
may be. Siemens states that : " The products of the com- 
plete combustion of 1 lb. of coal have a capacity for heat 
equal to that of nearly 17 lb. of fire-brick and (in reversing 
every hour) 17 lb. of regenerator brickwork at each end of 
the furnace per lb. of coal burned in the gas producer per hour 
would be theoretically sufficient to absorb the waste heat, if 
the whole mass of the regenerator were uniformly heated at 
each reversal to the full temperature of the flame, and then 
completely cooled by the gases coming in. But in practice by 
far the larger part of the depth of the regenerator chequer- 
work is required to effect the gradual cooling of the products 
of combustion, and only a small portion near the top, perhaps 
a fourth of the whole mass, is heated uniformly to the full 
temperature of the flame, the heat of the lower portion de- 
creasing gradually downwards nearly to the bottom. Three 
or four times as much brickwork is thus required in the 
regenerators as is equal in capacity for heat to the products 
of combustion. The best size and arrangement of the bricks 
is determined by the consideration of the extent of opening 
required between them to give a free passage to the air and 
gas, and a surface of six square feet is necessary in the 
regenerator to take up the heat of the products of combustion 
of 1 lb. of coal in an hour. 

" By placing the regenerators vertically and heating them 
from the top, the heating and cooling actions are made much 
more uniform throughout than when the draught is in any 
other direction, as the hot descending current on the one hand 
passes down most freely through the coolest part of the mass, 
whilst the ascending current of air or gas to be heated rises 
chiefly through the part which happens to be hottest, and 
cools it to an equality with the rest. 

" The regenerators should always be at a lower level than 



FURNACES FOR METALLURGICAL PURPOSES 245 

the heating chamber, as the gas and air are then forced into 
the furnace by the draught of the heated regenerator, and it 
may be worked to its full power either with an outward 
pressure in the heating chamber so that the flame blows out 
on opening the doors, or with a pressure in the chamber just 




PSi* 



Fig. 71. — Section of Siemens' Steel Melting Furnace, with Valves. 

balanced, the flame sometimes blowing out a little and some- 
times drawing in." * 

Roberts- Austen gives 14 to 15 square feet of regenerator 
brick surface as being necessary for each 2 lb. of coal 
burnt between two reversals. 2 

The arrangement of the valves is a matter of very great 
importance. The usual arrangement is shown diagram- 
matically in Fig. 71. The butterfly valve is the commonest 

1 Collected Works,' vol. i. pp. 227, 228 
2 Introduction to the Study of Metallurgy, p. 261. 



246 



FUEL 



form, but many other forms have been suggested for the 
purpose, and have been described in the technical journals. 
The regenerative furnace has many advantages. Though 




B, Working doors. 



Fig. 72. — F. Siemens' Furnace. 
E, Gas regenerators. D, Air regenerators. 
A, Roof. 



G, Gas port. F, Air port. 

















*C3 


...-{" "i 








Tfifo^fWMMffWWMMm 


3, li 








»^pr<<»^ 




jj 
















La 






m 








Psr — 






u 


M 


u |i 


k ^ 



the temperature in the furnace itself is very high the gases 
escape at a low temperature (212° F. to 300° F.), and there- 
fore the heat which 
they carry away is 
small and the 
efficiency of the fur- 
nace is high. The 
flame can be kept 
perfectly steady for 
any length of time, 
and it can be made 
oxidizing, reducing, 
or neutral as re- 
quired. Furnaces 
of this kind are now 
built of large size up 
to 40 feet long and 
15 feet wide. 

Very many modi- 
fications on the 
original form have 
been suggested. 
In 1884 Mr. Frederick Siemens pointed out that the de- 
pressed roof and small combustion space in the ordinary type 




Fig. 73.— Batho Furnace. 



FUENACES FOR METALLURGICAL PURPOSES 247 

of furnace was disadvantageous, and that it would be better 
to make the roof a flat arch, or .even to raise it in the centre 
instead of depressing it. He contended that in order to obtain 
a high temperature the gases should be allowed free space for 
combination, as contact with solid substances promoted dis- 
sociation, and if the surfaces were cold hindered combustion. 
He also pointed out that furnaces constructed on this plan, 
in which the heating was entirely by radiation instead of by 
contact, were much more durable. This form of arch has 
now become very general. Mr. Siemens also altered the 
arrangement of the ports, placing the air port vertically above 
the gas port and making it overlap on both sides. This 
arrangement is often called the " Hackney " port, the heavier 
air tending to deflect the flame down into the hearth. 

In another type of furnace, usually called the Batho fur- 
nace, the regenerators are placed outside the furnace and on 
the same level, this arrangement having several advantages, 
among others the greater ease of access to the regenerators. 
In the Radcliffe furnace the regenerators are placed on the 
top of the furnace, an obviously improper position. 

A new form of Siemens furnace was described by Mr. J. 
Head and Mr. P. Pouf in 1889, which differs very much in 
arrangements from the ordinary type. The gas producer is 
attached to and forms part of the furnace, and there are only 
two regenerators — those for air. 

Gas from the producer b passes through the flue c' and 
valve a' to the gas port, thence into the combustion chamber 
h' g' . Air for combustion passes through the regenerator a', 
by an air flue, the air h', into the combustion chamber, where 
it meets the gas and combustion takes place. The flame 
sweeps round the chamber e, the products of combustion pass 
away by h g, and go partly through the regenerator a and 
partly into the gas producer b, to be converted into combus- 
tible gas. From time to time the direction is reversed as usual. 

The products of combustion contain about — carbon 
dioxide 17 per cent, oxygen 2 per cent, nitrogen 81 per cent, 
and small quantities of water vapour. As they pass into the 



248 



FUEL 



gas producer they are at a very high temperature, and the 
carbon dioxide is at once converted into carbon monoxide. 
A jet of steam is blown into the producer to enrich the gas. 
The new form of furnace is said to lead to considerable 
saving of coal and also in labour and repairs, and is said to 
" regenerate both the heat and the products of combustion." 



3IEMENS FURNACE. 



f'SA 




Fig. 74. — New Form of Siemens' Regenerative Furnace. From J. I. and S. I. 

It has only been used for reheating and has not yet been 
applied to steel making. 

The Ideal Furnace. — Another type of furnace designed 
by Mr. Thwaite is known as the ideal furnace. In this, 
two regenerators only are used — those for air. They are 
placed at the top of the furnace and are heated by the 
upward passage of the products of combustion. The gas is 
passed direct from the producer to the furnace. Mr. Thwaite 
claims that this furnace is most economical. 



FURNACES FOR METALLURGICAL PURPOSES 249 
Other Forms of Regenerative Furnace. — Regenera- 




FlG. 75. — Thwaite's Ideal Furnace. 



tors of other forms than chambers filled with a chequer- work 




Fig. 76. — Gorman's Heat-restoring Gas Furnace. From D. K. Clark's Fuel. 

of bricks are sometimes used. In the Ponsard furnace the 
hot gases are made to circulate round perforated bricks, 



250 FUEL 

through the channels in which the gas or air to be heated is 
made to pass, and in Gorman's heat -restoring furnace the 
products of combustion are made to circulate round fire-clay 
tubes through which the cold air passes, it being made to 
traverse the tubes twice in different directions. This furnace 
has been used with success in several ironworks for reheating. 

Action of the Furnace. — The action of the regenerators, 
or recuperators as they are better called, is very simple. The 
temperature in the furnace is very high, and the products of 
combustion would escape at a high temperature and thus 
carry away a large amount of heat. The regenerators inter- 
cept this heat, and the gases escape comparatively cool, the 
heat being retained by the brickwork and given up to the 
incoming gases at the next reversal. 

Position of the Regenerators. — This is a point about 
which, as already mentioned, there is great difference of 
opinion. They are usually placed beneath the furnace. This 
position, however, is not always convenient, and it is subject 
to flooding and to moisture from the ground. They are also 
difficult of access, and air and gas may mix through the brick- 
work and thus cause serious loss. On the other hand, if the 
regenerators are isolated and cased with iron, the loss from 
radiation may be greater. 

The gases may be sent to the regenerator hot as they leave 
the producer, or they may be cooled. There is a general 
feeling that no advantage is to be gained by the former 
method of work, and it is attended with certain disadvan- 
tages. The gases as they leave the producer are charged 
with tarry matters which are partly deposited in the flues, 
and also with gaseous hydrocarbons from the coal. When 
the tarry matters and gaseous hydrocarbons are swept into 
the regenerators they are partially decomposed with deposi- 
tion of carbon, so that the heating power of the gas is 
diminished, and the chequer-work becomes choked with 
carbon. 

Hence in many cases the gas regenerator has been 
abandoned, the gas being passed hot into the furnace. 



FUENACES FOR METALLURGICAL PURPOSES 251 

Thermal Efficiency of Regenerative Furnaces. — 
M. Krause in 1874 published an investigation into the 
efficiency of a regenerative furnace, the results of which, 
converted into British units, are given below. 

The composition of the coal, deducting ash, as deduced 
from the composition of the gas, was : 



Carbon 
Hydrogen 
Oxygen 
Nitrogen 



84-38 
617 
6-90 
2-55 



The quantity of gas produced from 100 lb. of coal was : 

Carbon monoxide ...... 155*9 

Carbon dioxide ....... 42-4 

Hydrocarbons ....... 8*0 

Hydrogen ........ 3-7 

Nitrogen ........ 392-2 



602-2 



whilst 3-97 lb. of tar, soot, and water was deposited. 

To find the capacity of heat of these products it is only 
necessary to multiply the weights by their specific heats. 



Carbon monoxide 
Carbon dioxide . 
Hydrocarbons 
Hydrogen . 
Nitrogen 



155-9 x -2479= 38-66 

42-4 x -2164= 917 

8-0 x -5929= 4-75 

3-7 x 3-4046= 12-73 

392-2 x -2440= 95-69 

602-2 x -2673 = 161-00 



The formation of the gas in the producer evolved 



66-800 lb. C to carbon monoxide 
11-560 „ C to carbon dioxide 



300600 B.Th.U. 
168100 



468700 



The total heat of combustion of the coal for 100 lb. 
would be : 



84-38 lb. C to carbon dioxide 
5*2 ,, H to water 



1226900 B.Th.U. 
319900 



1546800 



252 FUEL 

Therefore Aaonin L x 100 or 33 per cent of the total available 
1546800 x 

heat is evolved in the producer. Much of this is carried away 

as sensible heat, and is lost as the gases cool in the tubes. 

The balance, 1078100 units, is evolved on combustion of the 

gas in the furnace. 

The products of combustion, allowing 20 per cent excess 

of air, are : 

Carbon dioxide 309-4 lb. 

Water 47-2 „ 

Nitrogen 999-5 „ 

Oxygen 30-2 „ 

1386-3 „ 

of which the capacity for heat can readily be ascertained. 

Units. 
Carbon dioxide .... 309-4 x -2164= 67-0 

Water 47-2 x -4750 = 22-4 

Nitrogen 999-5 x -2440 = 243-9 

Oxygen . . . . . 30-2 x -2182= 6-6 

1386-3 x -2452 =339-9 

That is to say, the products of combustion absorb 339-9 
units of heat for each degree rise of temperature. 

Distribution of Heat. — M. Krause analysed the work of a 
heating furnace at Soughland ironworks. The furnace 
heated about 18,000 lb. of iron in twenty -four hours, and the 
quantity of coal used was 4000 lb., or at the rate of about 
4-44 cwt. per ton of iron heated. 

The coal contained 10 per cent of ash, so that the 4000 lb. 
was equivalent to 3600 lb. of combustible matter. The 
valves were reversed every half -hour, so that between each 
reversal 75 lb. of combustible was burned, developing 
1160100 units of heat. 

Losses by the Chimney. — Suppose the gases to leave the 
chimney at 392° F., they would carry with them 339-9 x -75 
x 360 =91760 units of heat. 

Losses by Transmission through Walls of Regenerator. — 
This M. Krause calculated, assuming the gases to leave the 



FUKNACES FOE METALLURGICAL PURPOSES 253 

furnace at 2910° F., to be 27750 calories, or 110100 
B.Th.U. 

Heat absorbed by Iron. — To heat 18,000 lb. of iron to 
2910° F. from 32° in twenty-four hours, or 375 lb. each half- 
hour, its specific heat being -185, would absorb 375 x 2880 x 
•185 = 199800 units. 

Summary of heat evolution for each 75 lb. of coal : 



Conversion into gas and loss in cooling -tubes 
Loss by chimney ..... 
Loss by transmission through walls of re-~i 
generator ..... i 
Taken up by the iron .... 

Lodged in furnace and loss through walls . 



Units. 


Per Cent. 


382800 


330 


91800 


7-9 


110100 


9-5 


199800 


17-2 


375600 


32-4 



1160100 100-0 



Heat intercepted by Regenerators. — The products of com- 
bustion leave the furnace at 2910° F., and carry off 2880 x 
254-9 =734000 units in half an hour ; of these the chimney 
takes off 91680, and the walls of the regenerators take up 
110100, and the remainder 532200 is available for heating up 
the gas and air, so that if the regenerators are of equal size 
there would be 266100 stored up in each. The quantity of 
gas produced from 75 lb. of coal is 451-6 lb., of which the 
capacity for heat is 120-8 units for each 1° of temperature, 
so that these gases are raised to the average temperature of 
2236° F. 

The thermal capacity of the air, including the 20 per cent 
excess for the 75 lb. of coal, would be 588-2 lb., and its 
specific heat may be taken as -24, so that for each degree 
141-37 units of heat would be required, and the resulting 
temperature would be 1914° F. 

As it is desirable that the air and gas should be at as 
nearly as possible the same temperature, the air regenerator 
is preferably made larger, so as to give a larger heating 
surface. The heat carried forward by the gases is of course 
added to that obtained by the above combustion. 

The above calculations cannot pretend to be accurate, on 



254 



FUEL 



account of the uncertainty of our knowledge of the true 



Cold Gas Furnace, 




Ideal Furnace. 



Combustible 



sal^Gas generator 



Conduits or Flues 




FIG. 77. — Thwaite's Diagrams. 



specific heats of gases at high temperatures. They are 



FURNACES FOR METALLURGICAL PURPOSES 255 

useful, however, in indicating the method of arriving at a 
heat balance. 

Mr. Thwaite's Calculations. 1 — Mr. Thwaite has calcu- 
lated the efficiency of the regenerative furnace under three 
conditions : (1) the gas supplied hot from the producer, (2) 
the gas cooled in cooling -tubes, and (3) the ideal furnace ; and 
his results are given graphically in Fig. 77. It will be noted in 
these that no allowance is made for loss by radiation from 
regenerators or furnace, all this being calculated as useful 
work. 

Surface Combustion Furnaces. — In using a high tem- 
perature gas -fired furnace one observes that the velocity of 
combustion increases as the temperature of the fire-brick 
rises. The flames, which at first may protrude from the port- 
holes of the furnace, recede when the temperatures approach 
a bright orange heat, showing that more gas can be burned 
in a given time when the contact surface is very hot. Some 
surfaces have a greater power than others in inducing or 
accelerating combustion. 

Some years ago Professor W. A. Bone took up this sub- 
ject, and in collaboration with Messrs. M'Court, Wilson, and 
others elaborated a system of " surface combustion," as it 
has been called, whereby high calorific intensity is de- 
veloped, the refractory material used being maintained at a 
very high temperature, and thus producing a greatly in- 
creased radiation effect. 

In simple forms of surface combustion burners the air 
and gas are supplied under considerable pressure, the air 
being only slightly in excess of the quantity required for 
complete combustion. The mixture passes from a mixing 
chamber through a flat porous diaphragm made of fire-clay 
granules held lightly together by a flux. A short time after 
ignition the flame disappears, combustion taking place just 
inside the outer surface of the diaphragm, which attains, 
with gases low in inerts, a bright orange or nearly white 
heat. 

1 See Journal S. Staff. Institute, vol. vi. 







Fig. 78. — Bone and M'Court's Surface Com- 
bustion Muffle Furnace with Preheated 
Air. 



256 FUEL 

In a muffle furnace (Fig. 78) the muffle is surrounded 

with granulated carbo- 
rundum or other very 
refractory material, and 
for the highest tem- 
peratures the air may 
be reheated. The air-gas 
mixture must have suffi- 
cient velocity to avoid 
back-firing. 

Surface combustion 
gas -firing has been ap- 
plied to boilers of the 
marine type, and effici- 
encies as high as 90 per cent have been attained with 
recuperation. The boiler tubes are fitted with specially 
designed blocks of granulated 
refractory material. The heat 
transference is very rapid. The 
development of the gas - fired 
boiler is limited by the compara- 
tively high cost of the therm in 
the gaseous form. 

Furnaces using Town Gas. — 
In recent years there have been 
great developments in the use of 
town gas or coke-oven gas for in- 
dustrial purposes. The furnaces 
employed are generally of the 
most simple kind, and only in 
exceptional cases is there any 
attempt at recuperation. Tem- 
peratures of 1000° C. are attain- 
able without the use of any aid 
to the ordinary Bunsen burner. When higher temperatures 
are required, either air blast or compressed gas (or both) 
or some system of recuperation is used. Fig. 79 shows a 







Fig. 79.— Section of the 
" Revergen" Gas Furnace. 



FUENACES FOR METALLURGICAL PURPOSES 257 

modern reversing gas furnace. Fig. 80 indicates a good 
working arrangement for the firing of water-tube boilers by 
coke-oven gas. 

Furnaces for Liquid Fuel. — Furnaces using liquid fuels 
have not yet been used to any extent for metallurgical pur- 
poses, though they may be so in the future. 

In general there are two ways in which liquid fuels may 
be burned : 

1. The oil may be passed through a retort or coil of pipe 
heated in the furnace or by external heat, by which it is 




Fig. 80.— Gas Firing of Boilers. 



vaporized and the gas is burnt. Such an arrangement is 
merely a gas furnace in which the gas is made from oil. This 
process has the great disadvantage that it can only be used 
with oils which, on distillation, leave no solid residue, and 
few such are cheap enough to be used. 

2. The oil in the liquid form is injected by pressure 
through a jet into the combustion chamber in the form of 
a very fine spray, or is atomised by compressed air or steam 
by means of specially designed burners. In this way com- 
bustion takes place at once, and there is no deposition of 

(D107) S 



258 



FUEL 



solid residue. Two forms of burner for this purpose are 
shown in Figs. 81 and 82. 




Fig. 81. — Aydon's Type of Injector as used at 
Messrs. Field's. 

Fig. 83 illustrates one of these 
modern rather elaborate contri- 
vances used for atomising heavy 
oils or tar. The oil, air, and steam 
enter at o, a, and s respectively. 

Liquid fuel has been very suc- 
cessfully used for firing boilers, 
stationary, locomotive and marine, 
by means of these injector burners, 
but the use of liquid fuel has not 
made the progress for these pur- 
poses that many of its advocates 
expected until quite recently. 

Liquid fuel has, however, come largely into use for small 

furnaces, for 
metal melting 
and other pur- 
poses. These are 
of two types, re- 
verberatory fur- 
naces and cru- 
cible furnaces. 

Rockwell Fur- 
nace. — Of the 




Fig. 83.— Field-Kirby Automiser. 





Fig. 82. — Aydon's Type of Injector as used at Woolwich. 



reverberatory furnace type the Rockwell Furnace is perhaps 






FURNACES FOR METALLURGICAL PURPOSES 259 

the best known, although there are now several other forms 
on the market. This furnace consists of an iron cylinder 
lined with very refractory material, and narrowed at the two 
ends. At the one end air is blown in, and the other serves 
for the escape of the products of combustion. A charging 
opening is provided in the middle of the cylinder. When 
the furnace is in use this is held firmly in place by catches, 
and there is a hole in the centre through which the metal 
can be poured. Very frequently these furnaces are built 
double, the oil being supplied alternately at the two ends, 
and each furnace being capable of independent rotation. The 
usual capacity of these furnaces is about 1000 lb. of metal, 
though they may be built either larger or smaller. 

In 1905 Mr. Quigley read a paper before the Pittsburg 
Foundrymen's Association in which he described some experi- 
ments he had made with furnaces of this type, and he gave 
the following figures : 

Metal charged 7000 lb. 

Oil used, including that used in heating up . 93 gals. 
Oil used for 100 lb. of metal melted . .1*3 gals. 

Time required to heat up furnace starting cold 27 mins. 
Oil consumed in heating up . . .8 gals. 

Actual time furnace was in blast, including 

heating up . . . . . .7 hours 58 mins. 

Time per 100 lb. of metal melted . . 6*8 mins. 

Weight of metal per minute . . . 14*6 lb. 

Average time per head of 500 lb. . . 34 mins. 

The Steele - Harvey Furnace. — This is a crucible 
furnace fed with oil, and it may be built fixed (in which case 
the crucible is lifted out), or tilting, so that the crucible is 
poured without removing, the latter being in every way the 
best arrangement. The tilting furnace consists of a cylin- 
drical steel shell fined with refractory fire-brick carried on 
trunnions so that it can be tilted, or in some cases it is 
arranged so that it may be lifted away bodily by a crane. 
The crucible rests on a block of refractory material, and is 
wedged in position by side blocks. The mixture of oil and 
air is blown into the bottom by means of a suitable burner, 



260 



FUEL 



and burns in the space round the crucible. The furnaces are 
made with a capacity up to 750 lb. of metal. The lining 
stands about 500 heats, the crucible about 30 or more. The 
air is supplied at a pressure of about 40 lb. 

Mr. J. W. Krause, in a paper read before the Pittsburg 
Foundrymen's Association in 1905, gave the details of some 




Fig. 84. — Oil Furnace as applied to a Steam Boiler. 

experiments made with these furnaces at the works of the 
Maryland Steel Co. On a four days' test the figures were : 





Metal lb. 


Oil gals. 


Cost. 


Loss of Metal per Cent. 


1st day . 


. 1488 


32 


$0-80 


1-06 


2nd „ . 


. 2252 


56 


1-40 


1-19 


3rd „ . 


. 2579| 


65 


1-62 


1-96 


4th „ . 


. 2534 


62 


1-55 


'•03 




8853£ 


215 


5-37 


1*06 average per c. 



The cost of melting 100 lb., including oil and proportional 
cost of crucible, was 13-4 cents. 

Fig. 85 shows the arrangements of an oil-fired steel 
furnace. The oil is blown into the chamber a as a spray, by 
means of a steam jet, and is at once volatilized, entering the 
furnace and burning exactly like gas. 

Powdered Fuel. — Attempts have been made to burn 
nowdered fuel by a process almost identical with that used 
for spraying oil. In 1868 Mr. Crampton patented a method 



SUPPLY OF AIR TO THE FURNACE 



261 



of burning powdered fuel. The coal was powdered so as to 
pass through a 30-hole sieve, and the powder was blown into 
the furnace by means of a jet of air. The hearth of the 
furnace was so shaped that the currents were directed down- 
wards, and were reflected up again over the fire-bridge ; and 
a small fire was kept burning, at any rate until the tempera- 
ture of the furnace was high enough to ensure combustion 




Fig. 85.— Oil-fired Steel Furnace. 

taking place. Mr. Crampton described his methods in a 
paper read before the Iron and Steel Institute in 1873. A 
new form of burner for burning powdered fuel, invented by 
Mr. Carl Wegener, which promises well, is described in 
Engineering, vol. lxi. p. 81 (1896). 

In the United States there are now in existence boiler and 
other furnaces where a mixture of powdered coal and oil is 
sprayed in as the fuel. 



CHAPTER X 



SUPPLY OF AIR TO THE FURNACE — REMOVAL OF WASTE 
PRODUCTS — SMOKE — PREVENTION OF SMOKE 

Chimney Draught. — Reverberatory and all other open- 
hearth furnaces depend for the supply of air for combustion 
on natural draught, that is, on the draught producible by 
means of a chimney. The theory of the chimney is very 



262 FUEL 

simple ; it is simply that a column of heavy fluid will over- 
balance a column of the same height of a lighter fluid. In 
the chimney is a column of hot and therefore light air, outside 
is a column of cold and therefore heavier air, and the two 
are in communication at the bottom ; the pressure of the 
heavier cold air therefore displaces the lighter hot air, and 
flows in to take its place, but as it passes through the fire 
it too becomes heated, and thus a constant circulation is 
set up. 

About 24 lb. of air will be required to burn 1 lb. of 
coal, assuming the excess of air to be equal to that actually 
required, so that the products of combustion from 1 lb. 
of coal will weigh about 25 lb., and the volume may be 
taken as being about 12 J cubic feet at 32° F. for each pound 
of air passing into the furnace ; and as the volume of gas is 
proportional to its absolute temperature, the volume and 
pressure of gas can easily be calculated for any temperature. 
Rankine (Steam Engine, p. 286) gives an elaborate set of 
formulae, based to a large extent on the work of Peclet. As, 
however, Peclet 's constants were determined for special con- 
ditions, and it is uncertain how far they can be relied on 
under others, the formulae are not of much practical value. 

The active force which causes the circulation is the 
difference in weight of the two columns of air. The velocity 
of the current, neglecting friction, depends on the two factors, 
the height of the chimney, and the temperature of the gases, 
and varies as the square root of the increase in height and 
the square root of the difference of internal and external 
temperatures, and the actual value of v (the velocity) in feet 

per second, neglecting friction, is : v= * ^} — - — -, where g 

is the acceleration due to gravity = 32-2, h is the height of the 
chimney, T the temperature of the external air, t the tempera- 
ture of the chimney gases in F.°, and 459° the zero (0° F.) 
in the absolute scale, and if the velocity is constant, the 
amount of gas which will pass will obviously depend on the 
area of section of the chimney. 



SUPPLY OF AIR TO THE FURNACE 263 

It is calculated that the value of v reaches a maximum 
when the gas in the chimney has half the density of the 
gas outside, and therefore if the temperature outside were 
32° F., the gas inside should be at 459+32=491°, and 
the gas discharged will equal about 25 cubic feet per 
pound of air supplied, or about 600 cubic feet per pound 
of fuel. 

As the draught-power varies as the square root of the 
height of the chimney, each equal addition to the height 
makes less and less difference in the draught ; an increase, 
for instance, from 100 feet to 150 feet would only increase the 
velocity, if the temperature remained the same, in the ratio 
y/l : VF5, i-e. 1 : 122. 

As already mentioned, the friction of the gas and other 
resistances come into play and modify the results, and this is 
equivalent to a reduction of the area of the chimney. For 
round chimneys the effective area E may be taken as E = 
A - -6^ A, where A is the actual area. If additional resist- 
ances are to be overcome, as, for instance, thicker beds of 
fuel to be used or the gases be made to pass through more 
tortuous passages, a greater height will be needed to produce 
the same draught. 

The draught may be measured by the height of a column 
of hot air which would be required to balance the cold air, or 
by the pressure which it is capable of producing either in 
pounds on the square inch or in inches of water. The 
draught produced by a good chimney is about 1-5 inches of 
water, of which a large proportion is used in overcoming 
resistances of various kinds. The draught F, measured in 
inches of water, will be F = 192 h (D -d), where h is the height 
of the chimney, D and d the weight in pounds of a cubic 
foot of the air outside and the gas inside the chimney. As 
the draught or the velocity depends on both height of the 
chimney and the temperature of the gases it may be improved 
by increasing either. The height of the chimney can be 
increased by building it taller, the temperature can be in- 
creased by either preventing loss of heat from the gases or 



264 FUEL 

by preventing cooling by admixture of air. As a rule the 
draught in an open fire, such as a domestic grate or a roasting 
furnace, is very poor because of the large admixture of cold 
air which takes place, thus reducing the temperature of the 
gases, whilst in a crucible furnace, in which almost all the air 
passes through the fuel, and therefore the gases become 
intensely hot, the draught is very strong. 

In order to prevent loss of heat a chimney should be built 
as massive as possible, and should be of stone or brick, not of 
metal, which being a good conductor and also usually being 
thin, allows heat to be lost very readily. The height of the 
chimney will vary ; it should reach above surrounding build- 
ings, and as a rule should not be less than 50 feet, unless 
perhaps for small furnaces where there is but little resistance. 
Where there are resistances to be overcome, or where several 
flues pass into the same chimney, the height should be 100 
feet or more. 

The section of the chimney will, of course, depend on the 
amount of gas to be passed through, and this will depend on 
the grate area ; it should be about • 10 to -25 of the total grate 
area of the furnaces which feed it. A chimney 100 feet high 
and 30 inches in diameter, having therefore an area A =4-91 
square feet, and an effective area (A- •6y / A) = 3-58 square 
feet, should be capable of burning about 600 lb. of coal per 
hour. 1 

In metallurgical works the flues from the furnaces usually 
pass downwards into an underground flue, and several of 
these flues are attached to the same chimney. The greatest 
care must be taken in laying out the flues that at every 
junction the uniting streams of gas are travelling in the same 
direction, and if two or more flues unite at the foot of the 
same chimney, the chimney should be divided for some 
distance up, so that the currents may be all ascending before 
they mix. 

Blast or Forced Draught. — When air is supplied under 
pressure a very much more rapid combustion can be made 

1 See Kent, Trans. A.S.M.E., vol. vi. 



SMOKE 265 

to take place, amounting in some modern marine boilers to 
150 lb. per square foot of grate area per hour. 

The blast may be supplied in various ways. In the blast- 
furnace for iron smelting, blowing engines are largely used ; 
for smaller cupolas and for supplying the necessary blast to 
reverberatory furnaces, fans, blowers, or steam jets are pre- 
ferred. As a rule a blast is more economical than natural 
draught, as less excess of air need be passed in, and the gases 
can be allowed to escape at a much lower temperature. 

Removal of Products of Combustion. — However the 
combustion be brought about, whether by natural or forced 
draught, the chimney is necessarv to carry away the products 
of combustion. 

Smoke. — When coal, wood, or other similar materials 
burn they are very apt, under certain conditions, to form 
smoke. Smoke is simply unburnt carbonaceous material, 
and its production is always due to incomplete combustion, 
this being caused either by undue cooling or by lack of air. 

If the air supply be sufficient and the temperature high no 
smoke is produced, and in reverberatory roasting furnaces, in 
which these conditions are carried out, the flue dust is usually 
quite free from carbonaceous matter. On the other hand, in 
boiler fires where the cooling surface is large, so that the gases 
are easily reduced below the combustion temperature, the 
production of smoke is very common. 

It may be laid down as a general rule, that to ensure 
smokeless combustion three conditions are essential : 

1. The air must be in excess of that required for complete 

combustion. 

2. The air and gas must be thoroughly mixed. 

3. The temperature of the mixture must be kept above 

that necessary for combustion until all the carbon is 

consumed. 

The necessity for a sufficient air supply is obvious, but 

unless the air be brought in contact with the gas its presence 

can be of no value. A lamp may burn with a smoky flame in 

the free atmosphere, where therefore there is ample excess 



266 FUEL 

of air, but this air not being brought in contact with it at a 
sufficiently high temperature or rate of flow, combustion 
cannot take place. 

In practice smoke is almost always produced by undue 
cooling, and this may be brought about in various ways. 
One of the most common is bad stoking. A thick layer of 
cold coal is thrown on the fire ; the heat at once starts dis- 
tillation, but the evolved gases being separated from the hot 
fire by the cold layer of coal cannot ignite and therefore 
escape, producing a dense smoke, which is mainly not carbon 
but tarry matters. To prevent the production of smoke from 
this cause the fuel should be supplied in small quantities at a 
time at the front of the fire, so that the products of distillation 
pass over the hot coke at the back and are thoroughly heated. 
In some furnaces, and especially with some kinds of coal, a 
dead-plate — i.e. a plate with no perforations for air — is placed 
at the front of the furnace, and on this the fuel receives a pre- 
liminary coking before it is pushed forward into the furnace. 
In the case of furnaces driven with a blast below the hearth an 
additional supply of air should be sent in above the fire so as 
to ensure combustion of the gases. 

In order to ensure uniform stoking, mechanical stokers are 
often employed. By these the coal is either spread evenly 
over the fire, or it is supplied at a uniform rate on to a dead- 
plate, where it is coked, and then is gradually worked from 
the front to the back of the grate. 

Another very common cause of smoke is insufficient com- 
bustion space. The gases must be allowed to mix freely ; 
any contact with solid bodies will hinder combustion, and 
may determine the deposition of carbon. This takes place 
to some extent if the surfaces be hot, but to an enormously 
greater extent when they are cold, as in the case of boiler 
flues or tubes. 

The amount of solid material carried away by the smoke is 
not large, rarely amounting to 1 per cent of the fuel. It 
does not necessarily follow that the combustion of this soot 
would increase the heating power of the furnace, since for 



PREVENTION OF SMOKE 



267 



many purposes, especially for steam raising, a luminous highly 
radiative flame seems almost essential for economical work- 
ing, and it is impossible to have such a flame without at least 
the possibility of the formation of smoke. 

Soot. — When products of combustion carrying smoke 
come in contact with cold surfaces they deposit soot. Soot 
is a black mass, and is usually regarded as being carbon. It, 
of course, contains a large quantity of carbon, but it is by no 
means pure, as the following analyses will show : 





1. 


2. 


3. 


4. 


Carbon 


39 


86-94 


68-5 


75-3 


Hydrocarbons, etc. 


14-3 


3-3-5-2 


4-4 


3-9 


Hydrogen 










Sulphuric acid .... 


4-33 








Sulphur 






4-8 


3-2 


Mineral matter, etc. . 


36-67 


8-9-7 


22-3 


16-3 



1. Manchester Air Analysis Committee, Out-door Department. 2. Roberts-Austen 
Aspirated Fire Flue. 3 and 4. Cohen and Hefford. 

The presence of sulphur in the soot is of great interest. It- 
is at present not known exactly in what form it exists, but 
Cohen and Hefford think it is as organic sulphur compounds. 
They give the distribution of the sulphur in two samples of 
coal experimentally burned as being — 



Burnt, i.e. S0 2 in gases . 


. 


. 71-78 per cent 


60 per cent 


In cinder 


. 


. 13-71 „ 


28-12 „ 


In soot .... 




. 14-51 


11-88 „ 



The production of soot is far larger from house fires than 
from any form of furnace used in the arts. 

Prevention of Smoke. — Methods for the prevention of 
smoke have already been mentioned, but the only real remedy 
seems to be the larger use of gaseous fuel. It must not be 
imagined that gaseous fuel is necessarily smokeless ; far from 
it. Coal-gas can be made to give as smoky a flame as coal ; 
indeed, as before remarked, any luminous flame is at least 
potentially — and often actually, to a small extent — a smoky 



268 FUEL 

flame, but gas can be far more easily regulated than can a 
solid fuel fire. 

At the same time, though smoke may be prevented, the 
sulphur dioxide, sulphuric acid, and deleterious gaseous pro- 
ducts of combustion cannot be avoided, and can only be 
diminished by a less consumption of coal, or washing the coal 
to free it from pyrites, which is the chief sulphur-bearing 
impurity. 

CHAPTER XI 

PYROMETRY 

Pyrometry. — The measurement of temperature is the 
basis on which all knowledge of the quantitative effects of 
heating agents must be based, and yet it has been very much 
neglected, not only by practical but also by scientific metal- 
lurgists, and it is only within the last few years that serious 
attention has been given to it. 

The temperature of a body may be defined as " its state 
with reference to sensible heat," or, in other words, its hot- 
ness or coldness. The terms " hot " and " cold " are useful 
enough in popular language, but they are used so loosely 
that it is impossible to give them a precise value, and thus 
fit them for scientific use, and at best they are only com- 
parative. When the temperature of a body rises or falls, the 
body is said to become hotter or colder, and in this sense the 
terms may be used without fear of confusion, but they do 
not help us to understand what is meant by higher and lower 
temperature. 

The only explanation that can be given is that based on 
the transference of heat. If two bodies be placed in contact, 
either there will be a flow of heat from one to the other, or 
there will not. If there be not, then the bodies are said to 
be at the same temperature. If there be, then the body 
from which the heat flows is said to be at a higher tem- 
perature, and that to which it flows at a lower temperature. 



PYROMETRY 269 

Heat will always flow from a body at a high temperature to 
one at a lower temperature, until temperature equilibrium is 
set up, and both acquire the same temperature. The result- 
ing temperature will depend — provided there be no loss of 
heat — on the relative capacity for heat of the two bodies. 

On this law depend most of our methods of estimating 
temperature. The substance, the change in which is to be 
used to indicate temperature, and which may be called the 
thermometer, is placed in contact with the hot body, the 
temperature of which is to be taken ; interchange of heat 
takes place, and the thermometer acquires the temperature 
of the hot body, or rather a temperature resulting from the 
absorption of heat from the hot body by the thermometer 
itself. It is quite obvious that for any thermometer of this 
type to be of use, its heat capacity must be very small 
compared with that of the hot body, or it will so far reduce 
the temperature that the results which it gives will be 
valueless. 

Temperatures cannot be measured directly, as there is no 
scale that can be applied to them ; the sense of touch even, 
within the extremely narrow range for which it is available, 
is so vague and uncertain, so largely dependent on conditions 
other than temperature, that it is quite useless for measure- 
ment, or even for comparison. 

Heat produces many changes in material substances, and 
gives rise to many phenomena which can be readily measured, 
and which therefore may be used to measure temperature. 
Some phenomenon or property is selected which varies with 
the temperature, or which is " a function of the temperature," 
and the measurement of the change produced serves to 
measure the rise or fall of temperature producing it, for it 
must be remembered that it is only change of temperature 
that can be measured. If everything were at one and the 
same temperature, either high or low, there could be no 
means of measuring it. 

In order that various instruments of different construc- 
tion, or based on different principles, may be comparable, it 



270 FUEL 

is essential that there should be a definite zero or starting- 
point, and some suitable unit in which the measurements may 
be made, and these should be designed so as to be quite 
independent of any particular form of thermometer. 

There are in nature many fixed points, or changes taking 
place at a definite temperature, any of which could be taken 
as a convenient zero or starting-point. The one usually 
selected is the melting of ice or freezing of water. The 
temperature at which this takes place is taken as the zero on 
the Centigrade and Reaumur scales. The determination of 
the degree or unit may be made in several ways. The usual 
method is in principle as follows : The freezing-point having 
been selected as zero, another fixed point, usually the boiling- 
point of water when the barometer stands at 29-92 inches, is 
selected, and called 100. The difference between the freezing- 
and the boiling-point of water being taken as 100°, the value 
of a degree can easily be defined. If 1 lb. of water at 100° — 
the boiling-point — be mixed with 1 lb. of water at 0°, the 
result will be 2 lb. of water at 50°, since the heat which is 
lost by the hot water will be gained by the cold ; and similarly, 
if 1 lb. of boiling water be mixed with 99 lb. of water at 0°, 
the result will be 100 lb. of water at 1°. 

Hence a degree might be defined as that increase of tem- 
perature which would be produced by mixing 1 part of water 
at the boiling-point with 99 parts of water at the freezing- 
point, the experiment being so conducted that there is no loss 
of heat. This assumes the constancy of the specific heat of 
water. Or it may be defined as the temperature which will 
cause an expansion of mercury (or, better, air) y^ of that 
which takes place between the melting- and boiling-points of 
water. 

The figures given refer to the Centigrade or Celsius scale, 
which is in common use in Europe, and which is used every- 
where for scientific purposes. On the Fahrenheit scale, which is 
still generally used in this country, the freezing-point of water 
is called 32°, the zero being an arbitrary point not coinciding 
with any fixed point in nature, and the boiling-point is called 



PYROMETRY 271 

212°, the difference between the two being, therefore, 180°. 
On this scale the degree would be the increment of tem- 
perature produced by mixing 1 lb. of boiling water with 
179 lb. of ice-cold water (at 32°). The conversion of a tem- 
perature from one scale to another is very important and is 
very simple, if it be remembered that the ratio between the 
degrees on the two scales is 180 : 100, or 9 : 5. 

Conditions for a Good Pyrometer. — Having decided on 
the zero point and the degrees to be used, the conditions 
which will be required in a good pyrometer can be considered. 

1. It must indicate the temperature with sufficient 
accuracy for the purpose for which it is to be used. 

2. It must have a sufficiently long range. 

These are the fundamental and essential conditions, with- 
out which the instrument will be valueless. What degree of 
accuracy, and what range is necessary, can only be decided 
by a consideration of the exact conditions under which the 
instrument is to be used. It will be seen that a delicacy and 
range greater than that actually required will not only be 
useless, but will probably be attended with disadvantages in 
other directions. 

3. Its indications must be fairly rapid. 

4. It must always give the same indication at the same 
temperature, even after it has been a long time in use, i.e., 
there must be no displacement of zero. 

5. It should allow of comparison with the mercury or 
air thermometer, or with the fixed points of temperature, so 
that a value for its indications may be obtained in ordinary 
degrees. Failing this, the scale will be an arbitrary one. 

6. It should not be easily broken or put out of order, and 
should not be injured by being exposed to a temperature 
considerably above or below those which it is intended to 
indicate. 

7. It should not require a specially-trained man to make 
observations. 

8. It should be continuous in its indications — that is, it 
should not require a separate experiment for each observation. 



272 FUEL 

The degree of importance which will be attached to each 
of these conditions will vary with the purpose for which the 
instrument is required, and with the taste of the user. It 
must be admitted that there is no instrument which fulfils 
all the conditions, but there are several which fulfil most of 
them, and the engineer, knowing exactly what he requires, 
should have no difficulty in selecting an instrument to suit his 
purpose. 

Properties which have been used for Pyrometric 
Methods. — Almost every property of matter which varies 
with the temperature has been used or suggested as a basis 
for pyrometric methods. An exhaustive list has been given 
by Dr. Carl Barus, 1 to which those interested can refer. As, 
however, many of the methods suggested have not been 
applied to the production of instruments for technical use, a 
much briefer classification than that of Dr. Barus will answer 
the purpose here. 

1. Change of volume, i.e. expansion of solids, liquids, or 
gases. 

2. Vapour tension. 

3. Fusion. 

4. Method of mixtures. 

5. Conduction of heat. 

6. Optical methods. 

7. Electrical methods. 

8. Radiation of heat. 

In order that a phenomenon produced by increase of 
temperature may be available as the basis of a pyrometric 
method, it is essential — 

1. That the ohange produced by change of temnerature 
be capable of being measured. 

2. That the law connecting the change with the incre- 
ment of temperature producing it be accurately known for 
the temperatures at which the instrument is to be used. It 
is not sufficient that the law be determined, however ac- 
curately, for any other range of temperatures. 

1 Memoirs U.S. Geological Survey. 



PYROMETRY 273 

If a sufficient number of determinations be plotted suit- 
ably, and a curve be drawn through them, intermediate 
points may usually be obtained by measurements from the 
curve, but it is never safe to extend the curve in either 
direction beyond the extreme points which have been deter- 
mined by experiment. 

A large number of pyrometers have been devised based 
on changes of length or volume of selected substances pro- 
duced by the change of temperature. 

Expansion of Solids. — Many pyrometers have been 
based on the linear expansion of solids. If a bar of a solid 
be heated it will increase in length by a fraction of its length 
at 0° for each degree rise of temperature. For instance, a 
bar of iron 1 foot long at 0° would become 1-0000122 feet at 
1°, 1-0000244 feet at 2°, and so on. In general, a bar of 
length L at zero would become L(l + at) at t°, where a is the 
fraction by which the length of the bar, 1 unit long, would be 
increased by a rise of temperature of 1° C, or the coefficient 
of linear expansion. 

This formula would be quite correct if the value of a 
remained constant at all temperatures, whereas in fact it 
usually increases as the temperature rises. The amount of 
expansion is very small, so that unless the bar be very long 
it is not easy to measure, and a long bar is usually quite 
impracticable. 

Daniell's Pyrometer. — One of the earliest pyrometers 
suggested — that of Professor Daniell — was based on the 
expansion of a solid, and as the starting-point of such instru- 
ments it is of interest, though now of no practical value. 

It consisted of a tube of graphite, in which was placed a 
metal rod. The upper part of the tube was slightly enlarged, 
and in this portion was placed a tightly-fitting plug of 
porcelain pushed down so as to be in contact with the rod. 
The instrument was placed in the furnace or other space the 
temperature of which was to be determined, and allowed to 
remain long enough to acquire its temperature ; it was then 
removed and allowed to cool, As the temperature rose, the 

( D 107 ) -j- 



274 



FUEL 




bar, expanding, pushed the plug before it, and as the bar 

contracted on cooling, it could not draw the plug back again. 
The plug, therefore, remained in the position 
to which it had been pushed by the expand- 
ing rod, and by means of a measuring in- 
strument the distance by which it had been 
advanced could be measured. Obviously 
the observed expansion was differential — 
i.e. the difference between the expansion of 
the rod and that of the containing tube. 

Many attempts have been made to devise 
a practical pyrometer based on the expan- 
sion of solids. The instruments as a rule 
are very slow in their indications, and are 
not to be trusted except for very rough 
determinations. One of the best -known 
instruments of this type is that of Messrs. 
Schaffer and Budenberg (Fig. 86), which is 
based on the differential expansion of iron 
and copper. It consists of an outer tube of 
iron and an inner rod of copper attached 
to the bottom of it. The expansion of the 
copper being greater than that of the iron, 
the length which the copper rod projects 
will increase with rise of temperature, and 
this increase, which is of course very small, 
can be magnified by a system of levers and 
indicated by a pointer on a dial. 

As usually made the instrument indicates 
on the dial from 212° F. to 720° F. The 
tube is about 2 feet 6 inches long, and 
when placed in heating flues, or other posi- 
tions where the atmosphere is oxidizing, 

should be protected by a layer of clay. 

Expansion of Liquids. — This is the most common means 

of measuring temperature, but is not often available for very 

high temperatures. 



Fig. 86. 

Schaffer and Buden- 

berg's Pyrometer. 



PYROMETRY 275 

Mercury Thermometer. — This consists of a bulb con- 
taining mercury, to which is attached a stem with a very 
fine bore. When the bulb is heated the mercury expands 
and therefore rises in the stem, and as the capacity of the 
stem is very small compared with that of the bulb, a small 
expansion may produce a very considerable rise. The 
amount of mercury is so adjusted that it will not completely 
retire into the bulb at the lowest, or reach the top of the tube 
at the highest temperature to which the instrument is to be 
exposed. The instrument is always graduated by experi- 
ment : the bulb is put into melting ice, and the top of the 
column of mercury is marked 0° (or 32°) ; it is then put into 
boiling water or steam (the barometer standing at 29-92 
inches), and the height to which the mercury rises is marked 
100° (or 212°). The space between the two marks is (assum- 
ing the tube to be of exactly uniform bore) divided into 100 
(or 180) equal parts, each of which represents a degree. For 
temperatures above 100° C. (or 212° F.) the divisions are 
continued upwards as far as required, and for temperatures 
below 0° they are continued downwards. Temperatures below 
zero are read downwards, and are indicated by the sign - . 

Absolute Zero. — On the Centigrade scale the zero is the 
freezing-point of water, on the Fahrenheit scale it is a point 
32° F. below this ; both these points are arbitrary, and much 
lower temperatures than either are obtainable, so that the 
negative sign has to be used. Is there no more convenient 
starting-point ; is there no absolute zero, or point below 
which further cooling is impossible, so that if it were used 
as a starting-point the negative sign would never be required ? 
There is such a point, and though it has never been reached 
experimentally, it has been fixed by several lines of experi- 
ment and reasoning as being about 273° C, or 459° F. below 
zero. This point is called the absolute zero, and temperatures 
measured from it are called absolute temperatures. The 
absolute temperature can always be obtained by adding 273 
to the temperature in Centigrade degrees, or 459 to it in 
Fahrenheit degrees. 



276 FUEL 

Expansion of Mercury. — The amount of expansion of 
mercury which measures a degree is determined between 0° C. 
and 100° C, and higher and lower temperatures are obtained 
by continuing the divisions upwards or downwards ; but 
these divisions will only each represent the same increment of 
temperature, provided that the mercury expands at the same 
rate for all temperatures ; but it does not do so ; the co- 
efficient of expansion increases as the temperature rises. The 
mean coefficient of expansion of mercury between 0° C. and 
100° C. is -00018153, and even between these limits it is 
not absolutely uniform ; whilst at 300° C. the coefficient of 
expansion is -00019464, a difference of about 7 per cent. If 
great accuracy is required, a table of the variation at each 
particular temperature must be prepared. 

The question, however, is not quite so simple as would 
appear from this, for the mercury is contained in a glass 
bulb, which will expand and thus increase in volume. The 
observed rise of the mercury will not, therefore, be its ab- 
solute expansion, but will be the difference between this and 
the expansion of the glass. 

If a mercury thermometer be plunged into melting ice, the 
mercury falls to zero ; if it be then warmed and cooled again, 
and so on, a large number of times, it will be found that at 
last the mercury no longer returns to the point. The bulb 
has taken a permanent set, and produced what is called a 
displacement of zero. This will introduce an error into all 
readings, which may, in some cases, amount to as much as 1°. 

The mercury which the instrument contains, and the 
expansion of which is used in measuring temperatures, freezes 
at -38-9°C. (-38-0°F.), and boils at 357° C. (674-6° F.). 
These temperatures mark the extreme limits between which, 
under ordinary conditions, the instrument can be used. Its 
upward range is therefore very small, only reaching to about 
the melting-point of lead. 

Other liquids may be used so as to give a longer upward 
or downward range, according as the liquid has a higher 
boiling- or lower freezing-point than mercury. 



PYROMETRY 277 

The upper limit of a thermometer of this type is the boil- 
ing-point of the liquid ; if this could be raised, the range 
would be increased. The boiling-point depends on the 
pressure. If, therefore, the upper part of the tube were 
filled with some elastic fluid which would exert pressure, a 
somewhat higher range could be obtained. At a pressure of 
30 atmospheres the boiling-point of mercury is raised to over 
500° C. The great strength of the tube which would be 
required to prevent fracture prevents the extensive use of 
instruments based on this principle. Nitrogen-filled glass 
thermometers are made to register up to 540° C, but these 
do not stand prolonged heating owing to the softening and 
bending of the glass. Thermometers made of transparent 
silica instead of glass are not open to this objection, however. 

Baly and Chorley's Thermometer. — Messrs. Baly and 
Chorley have suggested the use of a liquid alloy of sodium 
and potassium, which has a very high boiling-point, and 
which can be used up to 600° C, and pyrometers on this 
principle are now made commercially. 

Expansion of Gases. — Very many pyrometers have been 
based on this principle, and the most diverse methods of 
utilising it have been proposed. Air pyrometers have some 
advantages, but in their usual forms they have also disadvan- 
tages, which often more than counterbalance the advantages. 

Gases expand very much more than either liquids or solids, 
and, what is more mportant, the rate of expansion is much 
more uniform, at least within very wide ranges of tempera- 
ture. In general the volume occupied by a gas is propor- 
tional to its absolute temperature, and the coefficient of 
expansion is nearly -003665 per C.°, but varies slightly for 
different gases. It is obvious that this is cubical expansion, 
or increase of volume, not mere increase of length, as in the 
case of solid bars. In all cases also the gas must be con- 
tained in an enclosing vessel, and the observed expansion will 
therefore always be the difference between the expansion of 
the gas and that of the enclosing vessel. The containing 
vessel also must be completely closed or cut off from contact 



278 FUEL 

with the outer air, and as the air in it has no visible surface, 
the use of a column of liquid or other index becomes essential 
if the expansion is to be observed directly. 

Regnault made a very large number of extremely accurate 
determinations of high temperatures by means of an air 
thermometer. His method was to heat the vessel containing 
the air to the temperature to be measured and to ascertain 
the quantity of air which was expelled. A globe of glass with 
a long neck, drawn out to a very fine point, was taken and 
put in the place the temperature of which was to be deter- 
mined. It soon got hot, and, owing to the expansion, a 
portion of the air was expelled. When equilibrium was 
attained the globe was removed, the neck sealed as rapidly 
as possible, and it was allowed to cool, the height of the 
barometer at the moment of sealing being noted. The neck 
of the globe was then broken off under mercury, and the 
globe with the mercury which had entered it was weighed. 
From this weight the volume of the air expelled could be 
calculated. The globe was then filled with mercury and 
weighed, and from this weight the capacity of the globe, and 
therefore the quantity of air it would contain, could be 
calculated from these data ; and making the necessary 
corrections for barometric pressure, expansion of the globe, 
etc., the temperature could be calculated. 

Deville and Troost used a similar method with porcelain 
globes in place of glass, and iodine in place of air. A method 
based on the expulsion of a volume of air by the vaporization 
of a known weight of a volatile solid or liquid, on the same 
principle as Meyers' method of determining vapour densities, 
has also been proposed. All these methods, however, neces- 
sitate trained observers, and involve an amount of calcula- 
tion which renders them quite unfit for technical work. 

Changes of pressure which have practically no effect on 
the volumes of liquids and solids have an enormous effect on 
the volume of gases. If a gas be heated and the pressure be 
maintained constant, it will expand at the rate indicated by 
its coefficient of expansion ; but if the gas be so enclosed that 



PYROMETRY , 279 

it cannot expand, then it will exert a constantly increasing 
pressure on the containing vessel. The action of heat on gases 
may therefore be measured either by keeping the pressure 
constant and measuring the increase of volume, or by keeping 
the volume constant and measuring the increase of pressure. 

In the constant - pressure methods a globe of glass of 
known capacity is connected by a capillary tube with the 
top of one leg of a graduated manometer, so arranged, by 
means of a flexible tube or otherwise, that the mercury can 
be brought to the same level in both legs, so as to ensure the 
gas in the globe being at the same pressure as the air outside. 
As the globe is heated the gas expands, and some of it passes 
out into the manometer tube. When the globe has attained 
the temperature to be measured, the manometer is adjusted 
so that the mercury stands at the same level in both legs, and 
the volume is read off. The calculations to be made are some- 
what complex, and must take into account the volume of 
cooler air in the top of the manometer tube, the barometric 
pressure, etc. 

In the constant-volume method a similar apparatus may 
be used, but as the temperature of the air in the globe rises 
the column of mercury in the manometer tube must be 
increased, so as to balance the expansive power of the air 
and keep it at a definite volume. 

In either case many precautions must be taken to guard 
against error. One source of error which it is impossible to 
overcome is the diffusion of gas through the bulb ; and for this 
and other reasons these methods are of little practical value. 

The methods as described can only be used up to the 
temperature at which hard potash glass softens, say 600° C, 
unless bulbs can be made of some other material ; glazed 
porcelain answers very well, so long as the glaze remains 
intact, which is not very long. Platinum metal, on account 
of its infusibility, might at first sight appear suitable, but it 
occludes gases, and also at high temperatures is porous to 
some furnace gases. Callander suggests * the use of bulbs 

1 J. I. S.I , 1892, vol. ii. p. 165. 



280 



FUEL 



made of pure silica ; and these are now obtainable com- 
mercially. Borosilicate glass has also been suggested, but 
has not a sufficiently high melting-point. 

Fusion Pyrometers. — The melting-points of all fusible 
substances are fixed and definite, and, once having been 
accurately determined, can be used as a means of estimating 
temperature. The simplest method of using the fusion of 
substances in pyrometry is to take a clay dish provided with 
a number of depressions or cavities, in each of which is placed 
a fragment of a substance — usually a metal or alloy — of 
known melting-point, care being taken that the melting- 
points have sufficient range to cover the temperatures likely 
to be met with. The dish is placed in the furnace or space 
the temperature of which is to be measured, left long enough 
to acquire the temperature, then withdrawn and examined. 
Obviously the pieces which have melted have lower, and those 
which have not melted have higher, melting-points than the 
temperature to which they have been exposed ; a minimum 
and maximum temperature is thus fixed between which the 
temperature to be determined must lie, and which will usually 
be a sufficiently close approximation for practical purposes. 

For determining the temperature of the hot-blast, the 
metals and alloys are made into coils of wire, which are intro- 
duced into the main, the temperature of which is to be taken. 

Among the metals and alloys suitable for this purpose the 
following may be mentioned, though the selection will 
obviously depend on the temperatures it is required to 

estimate. 

Metals 



Tin . 










M.P. 232° C. 


Bismuth 










„ 267° „ 


Lead . 










„ 328° „ 


Zinc . 










„ 420° „ 


Antimony 










„ 632° „ 


Silver . 










„ 961° „ 


Gold . 










„ 1064° „ 


Copper 










„ 1084° „ 



And by means of suitable alloys, the melting-points of which 
are known, other points can be obtained. 



PYROMETRY 



281 



One objection to this method is that the alloy can only be 
used once. 

Seger Cones. — For the determination of high tempera- 
ture a similar principle has been used, clay mixtures which 
melt at high temperatures being used in place of alloys. 
Seger cones are small pyramids, about 3 inches high, standing 
on a base f inch wide (a smaller size is also in use), and the 
fusibility of these is graduated, so that at the temperature 
marked on them the point of the pyramid bends over and 
touches, or nearly touches, the surface on which it stands. 

These and similar appliances are largely used in the pottery 
industry, bars of the clay mixture carried on supports being 
sometimes used in place of the cones. Seger cones are most 
useful as danger signals for high temperatures. The new 
scale of cone numbers and corresponding melting-points is 
as follows : 

Softening Points of Seger Cones 



Cone No. 


Cent. 


Fahr. 


Cone No. 


Cent. 


Fahr. 


017 


730 


1346 


11 


1320 


2408 


016 


750 


1382 


12 


1350 


2462 


015? 


790 


1454 


13 


1380 


2516 


014a 


815 


1499 


14 


1410 


2570 


013a 


835 


1535 


15 


1435 


2615 


012a 


855 


1571 


16 


1460 


2660 


011a 


880 


1616 


17 


1480 


2696 


010a 


900 


1652 


18 


1500 


2732 


09a 


920 


1688 


19 


1520 


2768 


08a 


940 


1724 


20 


1530 


2786 


07a 


960 


1760 


26 


1580 


2876 


06a 


980 


1796 


27 


1610 


2930 


05a 


1000 


1832 


28 


1630 


2966 


04a 


1020 


1868 


29 


1650 


3002 


03a 


1040 


1904 


30 


1670 


3038 


02a 


1060 


1940 


31 


1690 


3074 


Ola 


1080 


1976 


32 


1710 


3110 


la 


1100 


2012 


33 


1730 


3146 


2a 


1120 


2048 


34 


1750 


3182 


3a 


1140 


2084 


35 


1770 


3218 


4a 


1160 


2120 


36 


1790 


3254 


5a 


1180 


2156 


37 


1825 


3317 


6a 


1200 


2192 


38 


1850 


3362 


7 


1230 


2246 


39 


1880 


3416 


8 


1250 


2282 


40 


1920 


3488 


9 


1280 


2336 


41 


1960 


3560 


10 


1300 


2372 


42 


2000 


3632 



282 FUEL 

Method of Mixtures. — This method has been applied in 
many ways. The principle is that something is heated to the 
temperature which is to be measured ; then mixed with some 
other substance in such proportions as to produce a mixture 
the temperature of which can be measured by a mercury 
thermometer. 

In most instruments based on this principle the substance 
heated is a ball or cylinder of metal, which is cooled in or 
mixed with water the temperature of which is afterwards 
taken by means of a thermometer. 

Let W be the weight of the metal ball or other body, S its 
specific heat, T the temperature to be determined, W the 
weight of the water, t its temperature before the experiment, 
and t' the temperature of the mixture after the experiment. 

The heat lost by the hot body will be W x S x (T - 1')— 
that is, its weight multiplied by its specific heat and by its fall 
of temperature. The heat gained by the water will be its 
weight multiplied by its gain in temperature — that is, W x 
(t' - 1) ; and if there be no loss of heat these must be equal, 

so that WS(T-*') = W'(*'-*); therefore, T = W(t '^ + t \ 

whence T can be calculated, since all the other values are 
known. 

These formulae are of little value for high temperatures, 
because the specific heat of metals varies, and S can only be 
the mean specific heats between the temperatures, and this is 
not known till T is known. By the use of tables calculated 
for various temperatures this difficulty can be overcome. 

Instruments based on this principle are sometimes called 
specific-heat pyrometers, because the specific heats of the 
substances mixed must be known, and because the accuracy 
of the method depends on the assumption that the specific 
heat remains constant at the highest temperatures which 
have to be measured, an assumption which is certainly not 
absolutely correct. 

Siemens* Pyrometer. — The form of apparatus most 
commonly used is that of Siemens, Fig. 87, which consists 



PYROMETRY 



283 



of a copper vessel made with double walls, to avoid as far 
as practicable loss of heat. This is fitted with a thermometer 
and a set of copper or iron cylinders ; platinum would, of 
course, be better, but is very expensive. The cylinders are 
heated to the temperature which is to be determined, and 
are transferred as quickly as possible to the water, the tem- 
perature of which is taken without delay. 

This method, in spite of its obvious defects, was until 
recently the most accurate pyrometric 
method available, and it is fairly convenient 
for some purposes, though too troublesome 
for ordinary work. 

It is not continuous, a special experiment 
being required for each determination, and 
this takes some time, but does not require 
great skill in conducting it. There is always 
some loss of heat in removing the ball from 
the furnace to the water, however quickly 
it may be done, a loss which it is impossible 
to estimate, and which may vary very much, 
so that a single determination can never be 
relied on. If a furnace temperature is being 
taken, it is often difficult to fish out the 
ball. The result will always have to be 
calculated, tables being of little use, as the 
balls used change in weight, and must be 
weighed before each set of experiments. 

Krupp's Pyrometer. 1 — This instrument, which is used 
for the determination of the temperature of the hot-blast, is 
based on the principle of mixtures. The hot-blast is mixed 
with air at the atmospheric temperature in such proportions 
as to reduce the temperature of the mixture so low that it can 
be determined with a mercury thermometer. 

The blast enters at A, and is throttled down to a suitable 
pressure, which is indicated by the pressure-gauge pg, and 
rushes through the nozzle f, drawing in cold air through the 

1 Von Bergen, Journal Iron and Steel Institute, 1886, vol. i. p. 207. 




Fig. 87. 
Siemens' Pyrometer. 



284 



FUEL 



pipe P, the temperature of the inflowing air being registered by 
the thermometer t. The mixture of hot and cold air escapes 







Fig. 88. — Krupp's Pyrometer. 

at f, its temperature being indicated by the thermometer t'. 
The formula which gives the required temperature is 

H=c(F-A)+A, 

where H is the temperature required, 

A is the temperature of the cold air, 
F is the temperature of the mixture, 
c a constant depending on the pressure of the blast. 

Each instrument is graduated by comparison with a 
standard pyrometer. 

This instrument is said to be very successfully used at 



PYROMETRY 



285 



some Continental ironworks, and is obviously only suitable 
for taking the temperature of a current of hot gas supplied at 
a sufficient pressure. 

Conduction Pyrometers. — Several methods of measure- 
ment of temperature based on the laws of conduction have 
been suggested. The principle used is that of conducting 
away part of the heat, and, when the temperature is suffi- 
ciently reduced, measuring it by means of a thermometer. 

The method of Jourdes consists in inserting a bar of metal 
into the furnace the temperature of which is to be measured ; 
in the part of this bar projecting beyond the furnace are cup- 
like depressions containing mercury, in each of which a ther- 
mometer is placed, and from the temperatures indicated that 
of the furnace is calculated, the law according to which heat 
flows along a metal bar being known. Such methods are not 
capable of giving accurate determinations. 

Optical Pyrometers. — Several methods of thermal 
measurement have been suggested, dependent on the radia- 
tion of fight from strongly heated bodies. Indeed the rough- 
and-ready method of indicating temperature by its colour is 
based on this principle. We speak of a dull red heat, a red 
heat, or a white heat as indications of temperature. These 
terms are, however, .so vague that they are of little real value ; 
they depend entirely on the judgment of the individual, and 
are incapable of verification or measurement. Attempts 
have been made to fix definite temperatures corresponding 
to the colour indications. Those usually given are : 



Red heat .... 


525° C. 


Cherry-red heat 


800 „ 


Orange -red heat 


. 1100 „ 


White heat 


. 1300 „ 


Dazzling white heat . 


. 1500 „ 



These numbers are, however, only the very roughest 
approximations. As the change in colour depends on the 
nature of the rays emitted, the spectroscope would give 
valuable information, and no doubt a scale might be drawn 
up giving the approximate temperature at which particular 



286 



FUEL 



? 



iO ^> 



parts of the spectrum made their appearance as the tem- 
perature increased. 

Cornu - le - Chatelier Pyrometer. — This instrument 
(Fig. 89) depends on the comparison of the light emitted by 
the substance, the temperature of which is required, with that 
of a standard lamp, the brightness being taken as the test of 
temperature. It consists of two telescope tubes placed at 
right angles. One of these is for observing the body to be 
examined ; the other is for the standard 
lamp. 

The observing telescope has an ob- 
jective o, in front of which is an 
adjustable diaphragm or stop, and an 
eye-piece v. The rays from the lamp l 
are reflected by the mirror m into the 
eye-piece v, so that 
the two sources of light 
are observed together. 
As varying colour 
would interfere with 
the judgment of 
brightness, a mono- 
chromatic red glass is 
placed over the eye- 
piece. If the observing telescope be directed towards the 
object radiating light, the apparatus being so fixed that 
the image of a spot in the brightest part of the lamp flame is 
seen at the same time, two bright spots of light will be seen, 
one of which will probably be brighter than the other. The 
diaphragm or stop is adjusted until the two spots are equally 
bright, the size of the opening in the diaphragm is read off, 
and the corresponding temperature is obtained from a table. 
The brightness of the spot of light from the object being 
tested will depend on — 1. The temperature which is to be 
measured. 2. The distance of the luminous object. 3. The 
size of the opening in the top. The two last can be measured, 
and thus the first can be obtained. It is quite obvious that 




W r 



Fig. 89. — Cornu-le-Chatelier Pyrometer. 



PYROMETKY 



287 



the lamp must be quite constant, and the tables must be 
prepared by comparison with a standard pyrometer. 

The temperatures corresponding to the light intensities of 
a particular instrument are given below. The ratio will 
remain the same in all cases, though the actual temperature 
values will necessarily vary with the unit light, and the con- 
stants of each instrument. 



ntensity. 


Temperature. 
Deg. 


Intensity. 


Temperature. 
Deg. 


•00008 


600 


1-63 


1300 


■00075 


700 


3-35 


1400 


00466 


800 


6-7 


1500 


02 


900 


12-9 


1600 


078 


1000 


22-4 


1700 


24 


1100 


39 


1800 


64 


1200 


60 


1900 






93 


2000 



If the source of light is not at the standard distance, it 
must be borne in mind that the intensity varies inversely as 
the square of the distance. If the light be too intense for 
observation, it may be reduced by coloured glasses, the 
coefficients of absorption of which are known. 

A modified form of this apparatus is now made under the 
name of the Fery absorption pyrometer. The principle is 





Fig. 90. — F6ry Absorption Pyrometer. 



exactly the same, but absorption wedges which can be moved 
by screws are used to reduce the light to an equality with 
the standard lamp. The instrument is mainly useful for 




288 FUEL 

taking the temperature of small objects, such as incandescent 
filaments, for which the other pyrometers are unsuitable. 

Mesure and Noel's Pyrometer. — This instrument de- 
pends on the rotation of the plane of a ray of polarized 
light by a plate of quartz. In the tube of a telescope are 
fixed two Nicol prisms, or other polarizing apparatus, and 
between these a plate of quartz. If the analyser a be placed 
parallel to the polarizer P, and a bright object, illuminated 
by monochromatic light, be viewed, they will have no effect ; 
if they be placed at right angles, they will completely ex- 
tinguish the light, and the field will appear dark. If now a 

plate of quartz q be put 
between the Nicols, the 
field will be illuminated, 
and the analyser will have 
to be turned through an 
kg. 91. angle to cause extinction 

Mesure and Noel's Pyrometer. - ,. , mi . , ... 

of light. This angle will 
be that through which the quartz plate has rotated the 
plane of polarization. This angle depends on the thickness 
of the quartz plate, which is fixed for each instrument, and 
on the wave-length of the fight, which is a function of the 
temperature. If the light is not monochromatic, then, instead 
of absolute darkness, a series of colours will appear, and one 
definite tint is taken as the standard. 

The source of light, the temperature of which is to be 
measured, is viewed through the instrument, the analyser is 
rotated till the standard tint appears, the amount of rotation 
required is read off on the graduated circle, and the tempera- 
ture corresponding is obtained from a table. The results seem 
to be fairly accurate, and it is, at any rate, a convenient 
method of determining the temperature by inspection. 

Neither of the two last-described pyrometers is available 
below a red heat, and therefore they cannot be directly 
compared with the mercury thermometer. 

The Wanner Pyrometer. — "In this instrument the 
light emitted by the heated body, the temperature of which is 



PYROMETRY 



289 



being measured, is broken up by a train of prisms, and the 
spectrum is screened off so that only the red portion corre- 
sponding to the Fraunhofer C line is visible. The intensity 
of this is compared with that of the red radiation from a small 
6- volt electric lamp. The pyrometer has the external appear- 
ance of a telescope about a foot long ; at the end which is 
directed towards the furnace there are two slits, one of which 
is covered by the small electric lamp. When the instrument 
is directed towards the furnace, the field, as viewed through 
the eye-piece, is seen to be composed of two semicircles ; one 
of these is illuminated by the lamp, and the other by the light 
from the furnace. The two halves of the field can be ad- 
justed to equal intensity by rotating the analyser, which 



z 

Nicol Bipnsm 

■ * J W"""y"i 



Direct Vision Prism 




Objective Slits 

Liqhtfrom Furnace 



Lens / 

Oj Double Imaqe Prism 
1 w 

Fig. 92.— Wanner Pyrometer. 



—* ."Reflecting Prism 



Lamp A 



forms the eye-piece of the instrument ; and, from the angle 
through which the eye -piece has been turned to produce 
equality of colour, the temperature is ascertained by reference 
to a table. 

" Fig. 92 shows a vertical section through the instrument. 
The light which is emanating from the two sources a and b 
(lamp and furnace) passes through the slits s, s l5 which Jie 
in the focus of the lens o 1 ; it is broken up into its con- 
stituent colours by the train of prisms k, and is subsequently 
polarized by the Nicol's prism w ; the rays then pass through 
a double prism z, and are afterwards brought to a focus by 
the lens o 2 . Two images of a, due to the ordinary and 
extraordinary rays, and two of b are thus formed, but the 
prism z is so constructed that the image of A, due to the 
ordinary rays, coincides, in front of the eye-piece slit s 2 , with 
that of b, due to the extraordinary rays. On looking through 
the eye-piece the upper half of the field is seen illuminated 

(D107) U 



290 FUEL 

by rays from a, and the lower half by those from b, as the sets 
of rays are polarized in planes at right angles to each other, 
rotation of the analyser n has the effect of intensifying one 
half of the field and weakening the other. 

" The electric lamp must be adjusted periodically by 
comparison with the flame of a lamp burning amyl acetate. 
For this purpose it is placed on a horizontal stand with the 
uncovered slit directed to the flame of the amyl acetate. 
The analyser is set at zero, and the resistance in circuit with 
the lamp is adjusted so that the upper half of the field, 
illuminated by the electric lamp, has the same intensity as 
that of the lower half, lit by the amyl acetate flame. The 
instrument is then ready for use. The standard is the flame 
of amyl acetate, but as it would be impossible to apply it 
practically, on account of the flickering caused by draughts 
of air, an electric lamp is adjusted to this standard and used 
in its place. 

"Two forms of this instrument are made — one for 
measuring temperatures from 900° to 2000° C, and the other 
for the range 900° to 4000° C. The adjustment to equality 
of illumination can be easily and quickly made ; the error is 
approximately half a degree of rotation, which corresponds 
in the first of these instruments to about 5° at 1300° C, and 
14° at 1600° C." 1 

Electric Pyrometers. — Two of these are in use, depend- 
ing on quite different electric principles. 

The Siemens Pyrometers. — When an electric current 
is made to flow through a conductor, the conductor offers a 
certain resistance to its passage. This resistance increases 
as the temperature rises, the rate of increase varying with 
different conductors ; with platinum, which is almost always 
used, the resistance at 1000° C. is about four times as great 
as its resistance at 0°. This increase of resistance is easily 
measured, and if the law connecting it with the increase of 
temperature be known, a pyrometer can be readily based on 
this principle. 

i Prof, T, Gray, J.S.L.I., 1904, p. 1195. 



PYROMETRY 291 

The pyrometer will consist of three parts : 

1. The battery for producing the current. 

2. The pyrometer proper or coil, the resistance of which 
is to be measured. 

3. The apparatus for measuring the resistance. 

The battery may be of any form, but should be as constant 
as possible. As absolute constancy is unattainable, the 
reading apparatus must be compensated for small variations 
in the battery powers. 

The pyrometer proper consists of a coil of platinum wire 
wound on a cylinder of some refractory material, which is 
contained in an iron tube. Clay was at first used, but it has 
been found that after a time the elements present in the clay 
attack the platinum, render it brittle, and alter or destroy 
its conducting power. Mr. Callendar has suggested plates 
of mica as being the best material with which to make the 
core, as this does not cause any deterioration of the platinum, 
and also that it should be enclosed in a porcelain tube instead 
of an iron one. 

The apparatus for measuring the resistance is the most 
complex part of the instrument for accurate work. The 
method of determining the resistance almost always used is 
that known as the bridge method, which consists in adding 
accurately known resistances to the circuit till these are equal 
to the resistance to be measured. As this can be done with 
very great accuracy, the temperature can also be accurately 
determined. In other forms direct-reading apparatus, such 
as the Whipple Indicator made by the Cambridge Scientific 
Instrument Company, have been used, and recording appara- 
tus can also easily be applied. 

The instrument can be made to give readings over any 
required range, and may readily be compared with the 
mercury or any other standard thermometer. The law of 
the instrument must, of course, be known, in order to obtain 
accurate readings in degrees. Mr. Callendar states that the 
increase of resistance is nearly proportional to the absolute 
temperature. Readings can be obtained to ^° at 1000° C, 



292 FUEL 

and it is therefore one of the most delicate pyrometers 
obtainable. 

Le Chatelier Pyrometer. — This instrument, which was 
invented in 1886 by M. Le Chatelier, and which has been 
introduced and made popular in this country by Professor 
Roberts- Austen, is based on an entirely different principle. 
If bars of different metals be placed in contact, or soldered 
together at one end, the other ends being connected by a 
wire, and the joined ends be heated, a current will be found 
to flow through the wire. This principle has long been 
known, and was applied in the thermo-pile of Melloni, which 
has been much used in physical research, rods of bismuth and 
antimony being there used. It is quite obvious that, from 
the low melting-point of these metals, this instrument could 
be of no use as a pyrometer. 

In the Le Chatelier pyrometer, in place of these metal 
rods, wires of platinum and of an alloy of platinum with 
10 per cent of rhodium are used. The junction of these, when 
heated, gives rise to an electric current, depending on the 
difference in temperature between the hot and cold junctions, 
and, as this current can be measured, it gives a means of 
determining the temperature of the junction. It is essential 
that the relationship existing between the current and the 
temperature should be accurately known, and many investi- 
gators have been at work determining it. Dr. Carl Barus, 
who has thoroughly investigated the matter, comes to the 
conclusion that the current is very nearly, if not exactly, 
proportional to the absolute temperature of the hot junction. 

As the current to be measured is a feeble one, delicate 
apparatus is essential, a galvanometer of the reflecting type 
being always used where accuracy is required. The junction 
of the wires, which are either fused together or soldered 
with gold, and contained in a suitable protecting case, is 
placed at the spot the temperature of which is to be taken. 
As the junction gets hot the current flows and deflects the 
galvanometer needle, the position of which is read by the 
spot of light on the scale; or, if a permanent record is 



PYROMETRY 



293 



required, the spot of light may be made to register its move- 
ments on a strip of properly sensitized paper. This form of 
pyrometer has come largely into use, and has been popular- 
ized by the splendid work which Professor Roberts-Austen 
has done with it. He states that he is satisfied that it is 
accurate to 1° at temperature over 1000° C, and that it can 
be made to indicate T V° at 1000° C. 

The instrument is calibrated by determining the currents 
at known temperatures. The following may be taken as 
being fixed points sufficiently accurately known for the 
purpose : 



Boiling-point of water 






. 100° C. 


Melting-point of tin . 






• 232 „ 


„ „ lead 






. 328 „ 


Boiling-point of mercury . 






. 357 „ 


Melting-point of zinc 






. 419 „ 


Boiling-point of sulphur 






• 445 „ 


Melting-point of aluminium 






. 657 „ 


Boiling-point of selenium . 






. 690 „ 


Melting-point of silver 






. 962 „ 


gold 






. 1064 „ 


„ „ copper 






. 1084 „ 


„ „ nickel 






. 1452 „ 


„ „ platinum . 






. 1750 „ 



Whilst the principle on which this instrument is based is 
thus simple, the actual construction of the instrument itself, 
especially the indicating portion, is capable of very great 
variation. The light-spot method is unsuitable for many 
purposes, and several forms of direct-reading apparatus are 
on the market. In Messrs. Baird & Tatlock's pyrometer, for 
instance, the indicator is a " portable form of high -resistance 
dead-beat D'Arsonval galvanometer, the coil of which carries 
a long pointer over a graduated scale reading in degrees 
Centigrade and Fahrenheit." 

" The moving part is a rectangular coil delicately sus- 
pended between the poles of a powerful permanent magnet." 

Direct-reading instruments are also made by other 
makers. 

Several recording forms are also in use. In the Thread 



294 



FUEL 



Recorder of the Cambridge Scientific Instrument Company 
(Fig. 93) the paper to carry the record is stretched over a 

cylinder c which is made to rotate 
by clockwork as usual, and over 
this is an inked thread G. The 
boom of the galvanometer a is 
depressed every minute or half- 
minute, and, pressing the thread 
against the paper, leaves a mark. 
Fig. 94 shows the record obtained 
of the recalescence of eutectoid 
steel. 

In ribbon recorders the boom 

of the galvanometer is made to 

depress a point on to a ribbon, 

and in photographic recorders the needle casts a shadow on 

a slit behind which a band of sensitized paper is passing. 

Couples of iron, nickel, copper and alloys may be used, 




Fig. 93.— Thread Recorder. 

























"^ 






























































































90 


3 l C 










































































*». 


























































































































'i 




























































'i 










































80 


} l 










, 








I 




















































' 








• 


















































,, 












i 














































' 












i 






























































'', 




































70< 


i> 8 






1 






















1 


i, 






























































'■, 
































l 




























' 


•i, 






























i 
































, 




























































' 


i, 




















60 


r* 


i 


































































































'• 


, 




























































'« 


'. 
























































' 


•», 








































































sot 


>*| 


















































' t| 








in 



" 








K> 








Tl 


M 
20 


i 


IN 




vl 1 


Nl 
30 


^T 


E < 






40 










50 




'•n 


,., 


6C 



Fig. 94. — Heating and Cooling Curve of 0-9 per cent Carbon Steel. 



but they are not as durable as the platinum or platinum - 

rhodium couples, though they may produce a higher voltage. 

The couples require standardizing from time to time, 



PYROMETRY 295 

and the platinum and platinum -rhodium couple should 
never be exposed to furnace gases, as they attack the 
metals. 

These instruments require a trained and educated man to 
look after them, and cannot, therefore, be trusted to a work- 
man, and a special room for the reading instruments is 
necessary ; they are therefore more likely to be used for 
experimental work than for routine work, except in very 
large works. The most useful instrument is one having two 
scales for a dead-beat reflecting galvanometer, the lower 
scale reading to about 600° C, and employed with a base 
metal (copper constantan, for example) couple, and the 
higher scale reading to 1700° C. for use with a platinum 
platinum-rhodium couple. 

The Fery Radiation Pyrometer. — In the forms of 
apparatus described above the couple must be placed in the 
furnace the temperature of which is to be taken, and must 
itself become heated to that temperature. The Fery Pyro- 
meter is a modification of the thermo-couple pyrometer in 
which this is not necessary. It can be used for any tempera- 
tures above 600° C. 

The radiation which emanates from the hot body falls 
upon a concave mirror, and is thus brought to a focus. In 
this focus is a thermo-electric couple, the temperature of 
which is thus raised, and the increase of temperature is 
measured by the current generated. As the couple is never 
raised to a high temperature it is not liable to be destroyed or 
injured, and within wide limits the reading is independent of 
the distance which the instrument is placed from the source 
of heat. " It has been found, for example, that the reading 
obtained for the temperature of a stream of molten steel was 
precisely the same — 1200° C. — whether the instrument was 
set up 3 feet or 60 feet away." 

The apparatus is quite portable, and consists of the tube 
containing the couple, which is fitted with a telescope 
through which the object the temperature of which is to be 
taken can be observed, so as to get the instrument in the 



296 



FUEL 



right position, and a galvanometer for indicating the 
temperature. 

An adjustable diaphragm is fitted at the front of the tele- 
scope so that the amount of radiation falling on the couple 
can be regulated. Either a direct-reading galvanometer or 
a recorder may be used. The instrument has a very wide 
range of applicability. The temperature of the sun was 




Fig. 95. — Fery Radiation Pyrometer. 



determined by Professor Fery as being 2800° C, and the 
temperature produced by the iron " Thermit " reaction as 
being 2500° C. 

Fdry Spiral Pyrometer. — This is the simplest com- 
mercial instrument yet invented for measuring quickly and 
easily the temperature of any body above a dull red heat. 
It is only necessary to sight the instrument on the hot body, 
focus its image, and in a few seconds read the temperature 
indicated by the pointer on the dial. The instrument is 
completely self-contained, and although focused optically, it 
works on the purely mechanical principle of the difference 
in expansion of two metals. The heat rays are reflected by 
a mirror on to a spiral, built up of two dissimilar metals fixed 
together at one end, rolled flat together and very thin, and 
coiled into very small compass. The recording is done by 
a pointer attached to the free end of the spiral, which uncoils 
on being heated by the rays from the hot body. Extreme 
accuracy is not claimed for the instrument, but it is quite 



CALOKIMETRY 297 

serviceable for most commercial purposes, since by careful 
calibration an error of 1 to 2 per cent at 1000° C. is seldom 
exceeded. The chief limitation to its use is the inability 
to obtain a continuous record, and the reading is always 
low unless when sighted upon a " black-cold " body, such 
as charcoal. Its great advantages of easy manipulation 
and low first cost and upkeep render it highly useful in many 
instances of furnace management. 



CHAPTER XII 

CALORIMETRY 

Calorimetry is the measurement of quantity of heat as 
distinguished from thermometry or pyrometry, which is con- 
cerned only with measurement of temperature. Of the many 
cases in which heat measurement is required, it is only neces- 
sary here to deal with the measurement of heat evolved by 
combustion, that is, with the determination of the calorific 
power of fuel. 

Various forms of apparatus have been devised, from the 
time of Count Rumford till to-day, and all, except that of 
Berthier, depend on the combustion of a known weight of the 
fuel in oxygen, and the cooling of the products of combustion 
in a known weight of water. Some of the forms of apparatus 
have been designed only for extremely accurate work in the 
research laboratory, whilst others are intended for practical 
purposes. 

Berthier's Process. — This method stands alone in prin- 
ciple. It is based on the assumption that the heating power 
of a fuel is proportional to the amount of oxygen with which 
it combines, an assumption which, as already pointed out, is 
not correct. Berthier thus describes his process : * 

" Mix intimately one part by weight of the substance in the 

1 Traitd des Essais, 1828, as quoted by Percy, Fuel, p. 166. 



298 FUEL 

finest possible state of division with at least 20, but not more 
than 40, parts of litharge. Charcoal, coke, or coal may be 
readily pulverized, but in the case of wood the sawdust pro- 
duced by a fine rasp must be employed. The mixture is put 
into a close-grained conical clay crucible, and covered with 
20 or 30 times its weight of pure litharge. The crucible, 
which should not be more than half full, is then covered and 
heated gradually, until the litharge is melted and the evolu- 
tion of gas has ceased. When the fusion is complete, the 
crucible should be heated more strongly for about ten 
minutes, so that the reduced lead may thoroughly subside 
and collect into one button at the bottom. Care must be 
taken to prevent the reduction of any of the litharge by 
the gases of the furnace. The crucible while hot should 
be taken out of the fire and left to cool, and when cold 
it is broken, the button of lead detached, cleaned, and 
weighed." 

This process is quite useless, and does not give results of 
any value whatever. It is only mentioned because it has 
been so often recommended. 

Rumford's Calorimeter. — This is one of the very early 
forms of apparatus, and with it Rumford did good work. It is 
of historical interest, and being simple will serve to illustrate 
the principle on which all instruments for the purpose must be 
based. 

It consisted of a vessel of thin sheet-copper, 8 inches long, 
4J inches broad, and 4| inches deep, which was filled with 
water, and in it were three horizontal coils of a flat copper 
pipe, 1 inch broad and 1| inches thick ; one end, passing 
through the bottom of the box, had attached to it a copper 
funnel, and the other end projected above the water in the 
box. The substance to be tested was burned under and 
within the funnel, the products of combustion, passing through 
the coils, heated the water, and the rise of temperature gave 
the amount of heat absorbed by the water. The data re- 
quired for the calculation are — F the weight of the fuel con- 
sumed, W the weight of water, C the weight of copper in the 



CALORIMETRY 299 

instrument, S specific heat of copper, T initial temperature 

of the water, T" final temperature of water, H the heat 

evolved by the combustion of one unit weight of substance : 

then 

FH=(W+CS)(T'-T) 

„ (W+CS)(T'-T) 
.-.H = r . 

Bert helot's Apparatus. — This form of apparatus, which 
was formerly used in research work, consists of a cylindrical 
vessel of hard glass about 400 c.c. capacity, provided with 
two necks, one for the admission of oxygen and the other for 
the introduction of the substance to be burned. From the 
bottom of the vessel a glass spiral tube is made to wind, by 
which the gaseous products of combustion pass away. The 
apparatus is placed in 1000 c.c. of water contained in a 
platinum vessel. This vessel is supported on pieces of cork 
in an outer vessel of silver, which is itself contained in a 
double- walled vessel of iron, the space between the walls of 
which is filled with water. 

A small platinum crucible hung by a wire contains the fuel, 
and this is lighted either by a small piece of slow match or by 
dropping down a small piece of hot charcoal. The products 
of combustion passing away heat the water, and the result is 
calculated exactly as above. 

Thompson's Calorimeter. — This instrument is intended 
for technical work, for which purpose it is well adapted, and 
it has now come into general use. Its accuracy, however, is 
questionable. The fuel is not burned in oxygen, but in a 
mixture of potassium chlorate and nitrate which readily 
gives up its oxygen. 

It consists of a glass vessel graduated to contain 2000 
grammes of water, a copper cylinder e capable of holding the 
mixture of 2 grammes of fuel, with the necessary amount of 
fusion mixture ; a copper base, on which the cylinder can be 
placed, and a copper cylinder G, with a row of holes round the 
bottom, to be placed over it. This cylinder is held in place 
by a set of springs on the base, and is also provided with a 



300 



FUEL 



tube which reaches above the surface of the water, and which 
is fitted with a stop -cock. 

Two grammes of the fuel will require from 20 to 24 
grammes of the fusion mixture. 1 The mixture is put into 
the cylinder, tapped down, and placed on the base ; a piece 
of slow match is put on the top and lighted ; the cover G is 
quickly placed over it, and the whole is quickly put into the 
jar of water, combustion takes place, and the products of 
combustion pass up through the water and escape with a 
dense white smoke. Combustion once started should pro- 
ceed vigorously and 
should be complete in 
about two minutes. 
The stop -cock is then 
opened so as to ad- 
mit water into the 
interior of the cylin- 
der. This is raised 
quickly up and down 
once or twice so as 
to thoroughly mix 
the water, and the 
temperature is read 
with the thermometer J. The temperature having been 
taken before the experiment, the rise of temperature in F. 
degrees x 1000 gives the number of B.Th.U. absorbed by the 
water. 

There are various sources of loss — heat of decomposition of 
the fusion mixture, heat absorbed in warming the apparatus, 
and heat lost by radiation. To compensate for the last- 
named loss a blank experiment is first made, and then a 
second experiment, the water being cooled before starting 
about as much below the atmospheric temperature as it will 
be above it after. To allow for other sources of loss an 




Fig. 96. — Thompson's Calorimeter. 



1 The best fusion mixture is 3 parts chlorate of potash and 1 part 
nitre, and it and the fuel should be quite dry. The slow match is readily 
made by soaking ordinary wick in a solution of lead nitrate and drying. 



CALOMMETRY 



301 



addition of 10 per cent is made, which is said by the makers 
of the instrument to cover them. 

The glass vessel is usually also graduated to contain 1932 
grammes of water, and if that quantity be used, the reading 
gives at once the evaporative power of the fuel. For example, 



Temperature after experiment 

„ before experiment . 

+ 10 per cent 



61-5 
47-5 



14-0 
1-4 



15-4 x 1000=15400 



The quantity of combustion mixture required will vary with 
the nature of the fuel being treated, and charcoal, coke, or 
similar fuels should be burnt in a shorter 
and wider copper " furnace." 

Parr Calorimeter, Wild Calorimeter, 
etc. — In this type the fuel is mixed with 
sodium peroxide, Na 2 2 , and fired by 
a hot wire. In course of the reaction 
sodium carbonate is formed. From the 
total heat 27 per cent has to be deducted 
for this and other chemical reactions. 
The results are probably not of a high 
degree of accuracy. 

W. Thomson's Oxygen Calori- 
meter. — In this apparatus the fuel is 
burned in oxygen. The apparatus con- 
sists of a glass jar a capable of holding 
2000 c.c, or any other convenient known 
weight of water ; a platinum crucible g 
in which the fuel is burned, and which 
rests on a clay cylinder ; a bell-glass / 
which covers the crucible and contains 
the atmosphere of oxygen in which the 
combustion takes place. It is provided at the top with a 
neck, through which passes a glass tube i, by which the 
oxygen enters ; it is provided with a stop-cock k, and can 




Fig. 97. 
W. Thomson's Calorimeter. 



302 FUEL 

be raised or lowered as required. It rests on a perforated 
base, and is surrounded by a series of rings of wire-gauze to 
break up the ascending current of gas. A thermometer d 
and a stirrer j are suspended in the outer vessel of water. 

It is necessary to ascertain the heat capacity of the ap- 
paratus — that is, the amount of extra water to which the 
absorptive power of the apparatus is equal — which can be 
done once for all. 

Two thousand grammes of water, at about 25° F. above 
the temperature of the air, is poured into the apparatus, and 
the whole is well mixed. The water is left about the time 
which will be occupied by an experiment, and the amount 
by which the temperature is lowered gives the data for calcu- 
lating absorptive power of the apparatus sufficiently nearly 
for practical purposes. 

Thus, to take an example : 

Temperature of room, and therefore of the] 
calorimeter before water is added f 

Temperature of water .... 95° ,, 

Temperature after experiment . . 94° „ 

Therefore the fall of 2000 grammes of water 1° has raised 
the temperature of the calorimeter 11°, and the heat capacity 

of the apparatus is -y=- =182 c.c. of water. 

This weight must therefore be added to the amount of 
water used and the 2000 grammes calculated as 2182 grammes. 

To make a determination. 

About 1 to 1-5 grammes of the powdered fuel is carefully 
weighed and placed in the crucible, a short piece of slow 
match or an ignited vesta is placed on it, and the bell-glass is 
inverted over it. The whole is gently lowered into the water 
and the oxygen is turned on, the delivery tube being pushed 
down to near the fuel if necessary. Combustion at once 
begins. When combustion is over, the oxygen apparatus is 
disconnected and the stop-cock is opened so as to admit water, 
the bell-glass is moved up and down vigorously to ensure 
perfect mixture, and the temperature is taken, 



CALORIMETRY 



303 



Suppose 1 gramme of fuel were taken, and the rise of tem- 
perature of the water was to be -9°. Then since the 2000 
grammes of water is equivalent to 2182 grammes, taking into 
account the absorptive power of the apparatus, the calorific 
power is 

•9*9182 

= 1964. 



1 

This apparatus gives fairly good results. 

Several modified forms of this apparatus with improve- 
ments are now on the market, the best known being those of 
Rosenhain and Darling. In any case the oxygen used should 
be cooled to the atmospheric temperature before being passed 
into the combustion chamber. 

The Berthelot- Mahler Calorimeter. — This is a form 
of bomb calorimeter which is the only really satisfactory 




Fig. 98.— The Berthelot-Mahler Calorimeter. 

form of calorimeter for solid fuels. It is a modification of 
the bomb used by Berthelot in his classic researches on the 
heat of combustion of different substances. 

The combustion chamber b is of mild steel. It is 8 mm. 
thick, and has a capacity of about 600 c.c. It is enamelled 
inside and nickel-plated outside, and is provided with a cover 
in which is a valve for the admission of oxygen. Wires also 
pass through the cover, by which a short coil of iron or, better, 



304 FUEL 

platinum can be heated to ignite the fuel, which is contained 
in a platinum or silica crucible or capsule c. The whole is 
contained in a vessel of water d, provided with a spiral 
agitator s, and this again is placed in an outer vessel of 
water a. 

The fuel is weighed in the crucible, which is then fixed in 
position ; the igniting wire is weighed and adjusted, and the 
top is screwed down. Oxygen is allowed to enter from the 
cylinder o till the pressure on the gauge m indicates 25 atmo- 
spheres. The temperature of the water is noted at intervals 
of 1 min. for 5 mins., an electric current is passed from the 
battery p, and combustion takes place instantly. The tem- 
perature of the water is taken at intervals of half a minute 
until the maximum is reached, then observations are con- 
tinued at intervals of a minute for another 5 mins., the stirrer 
being kept going all the time. 

After the observations are completed the combustion 
vessel or " bomb " is washed out, and any nitric acid present 
may be determined volumetrically if great accuracy is 
required. 

It is necessary to determine the correction due to the loss 
of heat from the calorimeter during the test. The loss can be 
calculated by noting the rate at which the temperature rises 
or falls before firing and falls after firing. The addition to 
be made to the observed rise is generally not more than 
2 per cent, and can be calculated exactly from the periodical 
thermometer readings. The thermometer should be a very 
sensitive one, preferably a differential (Beckmann) thermo- 
meter, readable to 0-001° C. 

Then if A = the rise of temperature corrected, 

W =the weight of water in the calorimeter, 
W =the water equivalent of the apparatus, which 
must be determined by experiment, 
n =the weight of nitric acid, HN0 3 , 
/=the weight of the spiral of iron wire, 
•23 =heat of formation of 1 gramme of dilute nitric 
acid, 



CALORIMETRY 



305 



1*6= heat of combustion of 1 gramme of iron, 
x = the calorific power required, 
x = A(W + W) - (0-23 n + 1-6/). 

Fig. 99 shows the Mahler -Cooke bomb which embodies 
certain mechanical improve- „ 

ments. 

Calorimeters for Fuel Gas. 
— The Thomson oxygen calori- 
meter may be used for fuel gas, 
so can the Berthelot - Mahler 
form. In the latter the bomb is 
filled with gas before the oxygen 
is introduced, the pressure of 
oxygen required for coal - gas 
being about 5 atmospheres, and 
for producer - gas about 1-5 
atmospheres. 

Junker's Calorimeter. — This 
is one of the latest and best 
calorimeters for taking the calo- 
rific power of gases. A definite 
volume of gas is burnt, the 
amount consumed being 
measured by means of a meter, and a stream of water is kept 
flowing steadily through the apparatus. The volumes of gas 
and water and the rise of temperature of the latter supply 
the necessary data for calculating the calorific power. 

" A flame, 28 (Fig. 100), is introduced into a combustion 
chamber, formed by an annular copper vessel, the annular 
space being traversed by a number of copper tubes, 30. The 
heated gases circulate inside the tubes from the top to the 
bottom, whilst the current of water travels outside the tubes in 
the opposite direction, all the heat produced by the flame being 
thus transferred to the water, the spent gases escaping at the 
atmospheric temperature. The pressure of the water is kept 
constant by two overflows, 3 an<} 20, and the quantity of 

(D107) ' X 




Fig. 99.— Mahler-Cooke Bomb. 



306 



FUEL 



water is regulated by the stop-cock, 9. A baffle-plate, 14, 
at the lower end of the apparatus, secures an even distribu- 
tion of the water. The water can be passed through the 

tube, 21, into a measured 
receptacle. To prevent loss 
by radiation the apparatus is 
inclosed in a nickel - plated 
cylinder. In addition to the 
calorimeter a meter capable 
of passing y 1 ^ eft. for one 
revolution of the pointer, a 
water supply giving 1 to 3 
litres per minute, and two 
measure - glasses containing 
respectively 2 litres and 100 
c.c. are required. The 
quantity of gas burned should 
be regulated so as to give out 
about 1000 to 1500 calories 
per hour (4000 to 6000 
B.Th.U.), this is for illumin- 
ed/ ating gas 4 to 8 cubic feet, 
u =2^* or producer -gas 16 to 32 
cubic feet." 

The gas is lighted, the 
thermometer placed in posi- 
tion, and the water turned on. 
The temperature rises, and 
the mercury soon becomes 
stationary. As soon as the 
temperature is steady, the 
hot-water tube is shifted over the large measure-glass. As 
the water flows, the temperature indicated by the thermo- 
meter is noted from time to time. As soon as 2 litres of 
water have passed, the gas is turned off, and the quantity 
of gas which has passed is read. The following is an example 
given by the makers of the instrument : 




Gas Supply. 



Fig. 100.— Junker's Gas Calorimeter. 



CALORIMETRY 



307 



Meter Reading. 


Cold-water 
Thermometer. 


Hot-water 
Thermometer. 


Water. 


5 eft. 

5-344 eft. 
Mean 


8*77 
8-*77 


26-75 
26-76 
26-82 
26-80 
26-75 
26-80 


2 litres 


8-77 


26-77 


2 litres 



To be strictly accurate, the water should be weighed, as 
1 c.c. is not exactly equal to 1 gramme. 

If H = calorific power of one cubic foot of gas, 
W = quantity of water heated, in litres, 
T = difference in temperature between the hot and cold 

water, 
C = cubic feet of gas burned, 

or in the case given, 

When it is desired to know the net calorific value the 
quantity of water condensed should also be measured, as its 
latent heat must be deducted where the temperature of the 
products of combustion will, as in most cases, remain at a 
temperature above 100° C. The condensed water is drawn 
off by 35 into a measure-glass. In this case there was 53 c.c. 
of water. The latent heat of each c.c. may be taken as *6, 
so that the latent heat of the condensed water would be 



•6x53 



= 15-9, 



which must be deducted from the value obtained above, 
leaving 88*75 calories as the calorific power. 

Fig. 101 shows the new type of Junker's calorimeter. 

Boys' Gas Calorimeter. — This is another very good type 
of gas calorimeter which gives results differing from those 



308 FUEL 

of the Junker's calorimeter by not more than a quarter of 



INLET WATER 

THERMOMETER 

V 



LET OVERFLOW 
WEIR 




TO MEASURING VESSEL 
or TO DRAW CUP 



PARTITION BETWEEN 

AIR SPACES AND 

LOWER PRODUCTS CHAMBER 



FLAT INLET 
WATER PIPE 



Fig. 101.— Junker's Gas Calorimeter (new type). 



1 per cent. It is the instrument prescribed for gas-testing in 



CALORIMETRY 



309 



London by the Metropolitan Gas Referees, whose description 
is as follows : 

"The gas calorimeter which has been designed by Mr. 




Fig. 102. — Boys' Gas Calorimeter. 



Boys is shown in vertical section in Fig. 102. It consists of 
three parts, which may be separated, or which, if in position, 



310 FUEL 

may be turned relatively to one another about their common 
axis. The parts are (1) the base a, carrying a pair of burners 
b, and a regulating tap. The upper surface of the base is 
covered with a bright metal plate held in place by three 
centering and lifting blocks. The blocks are so placed as 
to carry (2) the vessel d, which must rest upon the horizontal 
portion of the blocks and not upon their upturned ends. 
The vessel is provided with a central copper chimney e and 
a condensed water outlet f. It is jacketed with felt r, pro- 
tected by a sheet of metal s. The diameter of the chimney e 
at the base is 3J inches and at the top 2J inches and its 
thickness -^ inch. The base of the outer vessel shown in the 
drawing as a separate piece is preferably spun in one piece 
with the chimney. In order to prevent obstruction of the 
flow of condensed water from the outlet F by the accidental 
contact of the thin brass protecting wall of the pipe system, 
a small dimple is punched in the outer casing on either 
side of the outlet f so as to project inwardly about T V 
inch. Resting upon the rim of the vessel d are (3) the water 
circulating system of the calorimeter attached to the lid G. 
Beginning at the centre where the outflow is situated there 
is a brass box which acts as a temperature equalizing chamber 
for the outlet water. Two dished plates of thin brass k k 
are held in place by three scrolls of thin brass lll. These 
are simply strips bent round like unwound clock springs, so 
as to guide the water in a spiral direction inwards, then out- 
wards, and then inwards again to the outlet. The lower or 
pendant portion of this box is kept cool by circulating water, 
the channel for which may be made in the solid metal, as 
shown on the right side, or by sweating on a tube, as shown 
on the left. Connected to the water channel at the lowest 
point by a union are five or six turns of copper pipe such as 
is used in a motor-car radiator of the kind known as Clark- 
son's. In this a helix of copper wire threaded with copper 
wire is wound round the tube, and the whole is sweated 
together by immersion in a bath of melted solder. A second 
coil of pipe, of similar construction, surrounding the first is 



CALORIMETRY 311 

fastened to it at the lower end by a union. This terminates 
at the upper end in a block, to which the inlet water box and 
thermometer holder are secured by a union as shown at o. 
An outlet water box d and thermometer holder are similarly 
secured above the equalizing chamber h. The lowest turns 
of the two coils m n are immersed in the water which in the 
first instance is put into the vessel d. 

" Between the outer and inner coils m n is placed a brattice 
Q made of thin sheet brass, containing cork dust to act as a 
heat insulator. The upper annular space in the brattice is 
closed by a wooden ring, and that end is immersed in melted 
rosin and beeswax cement to protect it from any moisture 
which might condense upon it. The brattice is carried by an 
internal flange which rests upon the lower edge of the casting 
h. A cylindrical wall of thin sheet brass, a very little smaller 
than the vessel d, is secured to the lid, so that when the 
instrument is lifted out of the vessel and placed on the table, 
the coils are protected from injury. The narrow air space 
between this and the vessel d also serves to prevent inter- 
change of heat between the calorimeter and the air of the 
room. 

" The two thermometers for reading the water tempera- 
tures and a third (u) for reading the temperature of the 
effluent gases are all near together, and at the same level. 
The thermometer u, divided on the Fahrenheit scale, is 
supported as shown in Fig. 102 by means of a cork and an 
open spiral of wire, so that the bulb is a short way above the 
circulating coil, and with its stem passing through one of the 
five holes provided for the effluent gases. The lid may be 
turned round into any position relatively to the gas inlet and 
condensed water drip that may be convenient for observa- 
tion, and the inlet and outlet water boxes may themselves be 
turned so that their branch tubes point in any direction. A 
wood shield t, made in two halves, serves to protect the 
outlet water box from loss of heat. 

" A regular supply of water is maintained by con- 
necting one of the two outer pipes of the overflow funnel 



312 



FUEL 



? 



to a small tap over the sink. The overflow funnel is 
fastened to the wall about 1 metre above the sink and the 
other outer pipe is connected to a tube in which there is a 
diaphragm with a hole about 2*3 mm. in diameter. This 
tube is connected to the inlet pipe of the calorimeter. A 
piece of stiff rubber pipe, long enough to cover the outflow 
water clear of the calorimeter, is slipped on to the outflow 
branch and the water is turned on, so 
that a little escapes by the middle pipe 
of the overflow funnel and is led by a 
third piece of tube into the sink. The 
amount of water that passes through 
the calorimeter in four minutes should 
be sufficient to fill the graduated vessel 
shown in Fig. 103 to some point above 
the lowest division, but insufficient in 
five minutes to come above the highest 
division. If this is not found to be 
the case, a moderate lowering of the 
overflow funnel or reaming out of the 
hole in the diaphragm will make it so. 
The overflow funnel should be provided 
with a lid to keep out dust. The 
graduated vessel (Fig. 103) shall have 
been previously examined and certified 
fig. los.-Graduated vessel. b y the Gas Referees. An impression 
of the stamp on the base of the vessel 
shall be accepted as proof that the vessel has been thus 
certified. 

" The thermometers for reading the temperatures of the 
inlet and outlet water should be divided on the Centigrade 
scale into tenths of a degree, and they should be provided 
with reading lenses and pointers that will slide upon them. 
The thermometers are held in place by corks (not india- 
rubber) making an air-tight fit within the inlet and outlet 
water boxes. Care must be taken that the bulbs are fully 
immersed." 



CALORIMETRY 



313 



There are several forms of recording gas calorimeters on 
the market. Some of these are not at all reliable. Others 




Fig. 104. — Simmance-Abady Gas Calorimeter. 

are very expensive and short-lived. The Gas Regulation 
Act, 1920, makes their use almost imperative. 



314 



FUEL 



Fig. 104 shows the construction of the ordinary Simmance- 
Abady gas calorimeter, and Fig. 105 (plate) the same 
apparatus adapted for recording the gross calorific value. 

Calorimeters for very Volatile Liquids. — For very 
volatile liquid fuels, such as petrol, the ordinary forms of 
calorimeter are, if not inapplicable, at least unsatisfactory. 
In such purposes a modified form of gas calorimeter is best 
suited, the fuel being burnt in a lamp. 

The " Darling " calorimeter is shown in Fig. 106. The fuel 
is burnt in the lamp a, which has 
a capacity of 3 or 4 c.c, fitted with 
an asbestos wick. The lamp is 
burnt in the bell - jar b, and is 
ignited electrically. The oxygen 
required is introduced by the 
tube I, and enters through the 
copper tube o, impinging on the 
top of the lamp. The products 
of combustion pass away by the 
tube t and bubble up through the 
water through holes in the per- 
forated base plate h. For very 
volatile liquids, such as petrol, the 
lamp is surrounded by cold water 
during combustion. 

This form of apparatus, or an 
adaptation of the ordinary gas calorimeter, gives satisfactory 
results. 

Comparison of Calculated and Determined Results. — 
For various reasons the results calculated from the various 
formulas are not exactly correct, the variation being some- 
times one way and sometimes the other. They are based 
on the assumption that the elements evolve the same amount 
of heat when burnt in the condition of combination in which 
they exist in the fuel that they would do if burnt in the free 
condition, which is obviously not correct. If the bodies in 
which they exist were formed with the evolution of heat the 




Fig. 106.—" Darling " Calorimeter. 




Fig. 108.— Simmance-Abady Gas Calorimeter adapted for 
recording the gross calorific value 



UTILIZATION OF FUEL 315 

results calculated from ultimate analysis will be too nigh, if 
with absorption of heat the calculated results will be too low. 
In the case of solid fuels the form of combination in which 
the elements are present is quite unknown, but probably 
they are mostly comparatively unstable, and so are formed 
with but little heat change. The same is true in the case of 
liquid fuels, but in the case of a gaseous fuel the proximate 
composition of which is known the calculated figures should 
be more accurate. A determination of the heating power by 
means of a calorimeter is always preferable to a calculation. 
Of the various types of calorimeter in use for solid and 
liquid fuels the Bomb is decidedly the most accurate, and is 
generally used where accuracy is required. It is, however, 
rather expensive and perhaps too complicated for ordinary 
technical use. Next to it stand the oxygen calorimeters, 
which, when carefully used, give good results, whilst the 
most generally used instrument, the Thompson calorimeter, 
with a fusion mixture, is not to be depended on except for 
rough approximations. 



CHAPTER XIII 

UTILIZATION OF FUEL 

Mechanical Equivalent of Heat. — Fuel is always 
burnt for the purpose of performing some useful work, very 
frequently for conversion into energy. A given amount of 
heat is equivalent to a given amount of mechanical energy, 
and the efficiency of any machine will be the proportion of 
this energy which is utilized or usefully employed. The 
mechanical equivalent gives the maximum amount of heat 
which it would be possible to obtain if there were no loss. A 
unit of heat is equivalent to 778 foot-pounds, so that the 
energy given out by one pound of water cooling through 1° F. 
would raise 778 pounds through a height of one foot if it 
could all be converted into useful work. 



316 FUEL 

First Law of Thermo - dynamics. — This may be thus 
stated : " Heat and mechanical energy are mutually con- 
vertible, and heat requires for its production, or produces by 
its disappearance, mechanical energy in the proportion of 
778 foot-pounds for each unit of heat." * 

Knowing the amount of heat which is evolved by the com- 
bustion of a fuel, it is quite possible for us to calculate the 
amount of energy it will give. Thus carbon, with its C.P. 
of 14,600, would give for each pound consumed 11,360,000 
foot-pounds of energy. 

An expenditure of energy at the rate of 33,000 foot-pounds 
per minute is called a horse-power, and the work done in one 
hour when working at the rate of one horse-power will there- 
fore be 1,980,000 units, which is called a horse-power-hour. 
It will be seen, therefore, that the combustion of one pound 
of carbon gives energy equivalent to about 5-7 horse-power- 
hours. From this statement it will be easy to realize the 
enormous amount of latent energy which is stored up in 
fuel. 

In practice, for various reasons, the whole of this energy 
can never be realized. 

Second Law of Thermo-dynamics. — This law, which 
is of equal importance with the first, may be enunciated : 
" It is impossible to transform any part of the heat of a body 
into mechanical work, except by allowing heat to pass from 
that body to another at a lower temperature." 

Conversion of Heat into Work. — Heat is converted 
into work by means of machines of various kinds, in which 
the heat is allowed to flow from a hot body to a cold one, and 
to do work as it flows. In general there are two classes of 
prime-movers in use, with both of which the metallurgist may 
have to deal. They are steam-engines and gas-engines. Both 
are essentially heat engines, but they differ in the way the 
heat is obtained and employed. 

The Steam Boiler. — In a steam-engine the first stage is 
to convey the heat of the fuel to steam, and this is done by 

1 Anderson, Conversion of Heat into Work. 



UTILIZATION OF FUEL 317 

means of a boiler. This is not a case of doing mechanical 
work, except in so far as the expansion of the steam may do 
work, but is merely the transference of the potential energy 
of the fuel into potential energy in the steam through the 
medium of combustion, a transference which can never be 
effected without great loss. 

The sources of loss which render it impossible to convey all 
the heat into the steam are many : 

1. The furnace gases must escape at a sufficiently high 
temperature to create a draught, and as each pound of fuel 
requires about 25 lbs. of air for its combustion, this must 
always be very considerable. Assuming the temperature to 
be 400° F., which will be much lower than usual, and the 
specific heat of the gases to average -25, this will amount to 
25 x 400 x -25 =2500 units for each pound of coal consumed, 
or, say roughly, 20 per cent. 

2. Loss of heat by transmission into the walls and by 
radiation may be guarded against, but can never be entirely 
prevented. 

3. There is always loss by ashes falling hot from the fire- 
bars, ashes containing carbon, etc. 

4. Evaporation of water in the fuel entails a loss in the 
heating power which is often very considerable. 

5. There may also be loss due to the formation of smoke, 
and to imperfect combustion, unburned combustible gases 
escaping with the products of combustion. 

In order that a boiler may be efficient it is necessary that 
combustion should be complete, and that the temperature of 
the fuel bed, and hence also the radiation, should be as high 
as possible. 

The examples of tests of boilers on p. 318 will show the 
measurements that are necessary, and the results which were 
obtained in 1895. 1 These results can at the present day be 
greatly improved upon. In boiler tests it is not uncommon 
to get 75 per cent thermal efficiency from a Lancashire and 
80 per cent from a water tube boiler with accessories. 

I G ; C. Thpmson, Pro. I. of E. and S. of S., 1895 f 



318 



FUEL 





1. 


2. 


3. 


Boiler 


1 Lancashire, 


1 Galloway, 


Babcock and 




7 x 26 feet. 


7 x 28 feet. 


Wilcox Tubulous. 


Heating surface .... 


570 sq. ft. 


905 sq. ft. 


2756 sq. ft. 


Fire-grate area .... 


34-66 


321 


45 


Steam pressure average, lb. . 


35-75 


621 


54 


Temp, of feed-water, average. 


135-2° F. 


48-9° F. 


126° F. 


Feed-water per hour, lb. 


3554-5 


6202 


11604 


Name of coal .... 


Earnock tripping 


Greenfield dross 


Daldowie tripping 


Condition 


dry and clean 


small and nut 




Fuel analysis] gf ; ; 


45-78 
54-22 


47-34 
52-66 


46-25 
53-75 


,, „ ultimate, C . 


6505 


60-22 


65-00 


H . . 


4-49 


4-40 


4-38 


. 


10-78 


9-29 


8-34 


N . 


1-78 


1-96 


1-61 


S . 


•54 


•75 


•81 


ash. 


9-70 


1318 


9-72 


moisture 


7-66 


10-20 


1014 


Fuel, specific gravity 


1-250 


1-293 


1-304 


Fuel used per hour, lb. . 


694-4 


918-4 


2132-85 


Per cent of ashes and clinker . 


9-67 


13-62 


7-70 


Thickness of fire 


6-8 inches 


8 inches 


15 inches 


Fuel burned per sq. ft. of ) 
grate surface per hour . . f 








2003 


28-61 


47-39 


Temp, of gases .... 


407° F. 


633° F. 


839° F. 


Speed of air entering, feet per ) 
min J 








531 


744 


798 


Carbon monoxide in gases 








Ratio of air used to theoretical ) 
quantity 1 








1-69 : 1 


1-65 : 1 


1-75 : 1 



Heat Expenditure. 


B.Th.U. 
Per Cent. 


B.Th.U. 

Per Cent. 


B.Th.U. 
Per Cent. 


Utilized in heating water 

Loss by gases 

Loss by imperfect combustion 
Loss by moisture in fuel 
Loss unaccounted for . 

Calorific power, B.Th.U. 

Practical heating power 
Theoretical heating power . 
Per cent used 


5448 46-17 
5326 44-36 

*94 -80 
1024 8-67 


7823 70-79 
1901 17-19 

135 1*22 
1145 10-36 


5873 5003 
3358 28-61 

144 1-23 
2363 2013 


11892 10000 

6-92 
11-66 
59-4 


11004 10000 

6-22 
10-96 
56-8 


11738 10000 

7-26 
11-84 
61-3 



The Steam-engine. — This is a machine for converting 
the energy in the steam obtained from the combustion of the 
fuel into work. It usually consists of a cylinder in which a 
piston is fitted steam-tight, but so that it can move freely 
backwards and forwards. Steam is almost always admitted 
alternately at each end of the cylinder, so that a reciprocat- 
ing motion is imparted to the piston which can be converted 
into the circular motion usually required by any suitable 
mechanism. 

The potential energy of the fuel has been transferred in 



UTILIZATION OF FUEL 



319 



part to the steam, and by the steam-engine part of the energy 
can be reconverted into work. 

In actual practice the consumption of steam varies from 
10 lb. per H.P. hour, in the best triple-expansion or large 
turbine condensing engines, to 60 lb. in small simple non- 
condensing engines. It is easy to see the many sources of 
loss by which the realization of anything like the full value 
of the steam energy is prevented without going into details 
of the methods of working. As we have seen, the efficiency 
of boilers is rarely much more than 75 per cent, and taking 
the efficiency of the best engine as 20 per cent the combined 
efficiency obtained from the fuel will be only -75 x20 = 15 
per cent. 

Amount of Fuel used per H.P. — One pound of coal, as 
has been shown, may have a calorific power of say 12000 
B.Th.U., which is equivalent to 9,336,000 foot-pounds, which 
is equivalent to about 4-5 H.P. hours ; i.e. the combustion 
of 1 lb. of fuel should give a power of 4-5 H.P. for one hour. 

The following examples given by Mr. J. W. Hall, 1 Nos. 6 
to 9 being quoted from Prof. Unwin, will show how far this 
has actually been obtained : 





Steam per 
I. H.P. hour. 


Coal per 
I.H.P. hour. 


1. High-pressure non -condensing engine ; 100 \ 

lb. pressure ; 50 H.P. nominal . . . j 

2. High -pressure non -condensing engine ; 1201 

lb. pressure ; 40 H.P. nominal . . . / 

3. Triple-compound non-condensing engine ; \ 

180 lb. pressure ; 30 H.P. nominal . . j 

4. Compound condensing engine; 100 lb. \ 

pressure ; 30 H.P. nominal . . . j 

5. Triple -expansion condensing engine ; 160\ 

lb. pressure ; 20 H.P. nominal . . / 

6. 7 Indicated H.P. 


32 
24 
20 

18 
14 


4-27 
3-20 
2-66 
2-46 

1-86 

8 

H 

2f 

2 


7. 10 „ „ 




8. 50 „ „ 




9. 200 „ „ 









With the advent in recent years of steam turbines of 
10,000 H.P. and the most economical methods of steam 

1 P. S. Staff. Institute of Iron and Steel Works Managers, 1894-1895, p. 41. 



320 FUEL 

raising the best power installations can work on full load at 
a consumption of 1-4 lb. of coal per brake horse-power-hour. 
This great improvement in the conservation of coal in the 
production of power is only possible by paying careful atten- 
tion to the design and equipment of the whole installation. 
Not only must the most efficient engines be utilized — and for 
large powers of over 2000 brake horse-power turbines have 
the preference — but the steam must be condensed at the 
highest possible vacuum, and the condensed water returned 
to the boiler. Most important is the use of economizers. 
These are usually sets of vertical cast-iron pipes placed in the 
waste gas flues, through which the boiler feed-water is made 
to circulate. The water should thus attain a temperature of 
about 200° F. In some cases air economizers are used with 
success. The steam is superheated to eliminate losses 
through wet steam in the engine and to enable it to be 
carried without loss. Water-feed regulators constitute 
another economy ; these automatically maintain a constant 
level in the boilers. Water circulators are another adjunct 
which effect a slight economy. 

It is highly important, finally, that combustion of the 
fuel should take place with the minimum excess of air, at 
any rate the percentage of carbon dioxide in the waste gases 
leaving the boiler furnace should not be less than 12 per cent. 
With good economizers it is then possible to reduce the tem- 
perature of the gases entering the stack to about 360° F. 
A boiler efficiency without the accessories may not exceed 
65 per cent, but chiefly owing to the effect of the economizers 
this may be brought up to 80 or even slightly more. 

Gas-engines. — The gas-engine is another means of con- 
verting the potential energy of fuel into actual energy. In 
this machine a piston and cylinder are provided, but instead 
of admitting steam behind the piston, a mixture of gas and air 
is admitted, which being exploded forces the piston forward. 
In the Otto engine the impetus due to the explosion is 
given only every fourth strode. The Otto cycle consisting of 
four stages : 



UTILIZATION OF FUEL 



321 



1. The piston makes a forward stroke and draws in a 
supply of gas and air through a valve in the rear of the 
cylinder. At the end of the stroke the valve closes, and 

2. The piston makes a return stroke, and compresses the 
air and gas into a chamber at the rear end of the cylinder. 

3. The explosive mixture, consisting of gas and air, and 
the residue of the products of combustion of the previous 
stroke, is ignited, very rapid combustion rather than explosion 
takes place, and is barely complete before the piston reaches 
the end of its second forward stroke. The heated gases 
expand, giving out work, and accelerate the motion of the 
moving parts. When the end of the stroke is nearly reached 
the exhaust-valve is opened, and 

4. The piston in its second return stroke partially drives 
out the products, and restores everything to the condition it 
was at the beginning of the cycle. 

It will be seen that here the energy of the fuel is used 
directly, without the intervention of the wasteful boiler, and 
as the temperature of the burning mixture is very high, the 
conditions are favourable for the utilization of a large amount 
of energy. The temperature of the cylinder, however, be- 
comes very high, and has to be cooled by a water-jacket, the 
water from which carries away from 30 per cent to 50 per cent 
of the heat. 

That gas-engines are much more economical than steam- 
engines is shown by the following table of engines worked 
with Dowson gas : 



Type of Engine. 


H.P. 


Fuel per H.P. Hour 
in pounds. 


Crossley 


199 


1-23 


„ ... 


210 


1-00 


,, ... 


170 


1-4 


Otto .... 


52-25 


1-67 


Atkinson 


16-7 


106 


Tangye 


100-6 


10 



Any combustible gas may be used. Coal-gas is largely 
used ; but good producer-gas, provided it be free from tarry 

( D 107 ) y 



322 FUEL 

matters, answers equally well, gas made in the Dowson 
producers being very often used. 

Blast-furnace Gas in Gas-engines. — Washed blast- 
furnace gas can readily be used in gas-engines, as it is quite 
free from tarry matter, and is quite as good as most producer- 
gas ; and as in all ironworks there is more gas than is required 
for ordinary purposes, even with the wasteful method of using 
via the boiler and steam-engine, it would seem that a useful 
outlet could be found for the energy in some manufacturing 
operations. It is used with great economy and success in 
works which combine bye-product coke-ovens and blast- 
furnaces, the surplus coke-oven gas being in some cases 
mixed with the blast-furnace gas. 

Oil-engines. — In the Priestman engine, which is one of 
the best known of these, the Otto cycle is used, but instead 
of gas a fine spray of petroleum or other oil, -780 to -812 
sp. gr., and having a flash-point not less than 75°, is forced 
in by means of compressed air. The waste heat is used in 
vaporizing the oil. 

In the best modern types of Diesel oil-engines almost any 
kind of oil, even thin coal-tar, can be used. The consumption 
of oil is sometimes as low as 0-35 lb. per brake horse-power. 



CHAPTER XIV 

TESTING FUELS 

Fuels to be tested. — The fuels to be tested in the labor- 
atory are coal, coke, oils, and gaseous fuels. A mere chemical 
analysis is not what is usually required, but an examination 
such as will enable an idea to be formed as to the actual value 
of the fuel for the purposes for which it is to be used. 

Proximate Analysis of Coal 

Moisture. — A rough estimate is obtained by powdering 
the coal as quickly as possible, weighing out about 5 grammes 



TESTING FUELS 323 

on a watch-glass, drying in an oven at 105° C. for an hour, 
cooling in a desiccator, and weighing with the watch-glass 
covered to prevent access of hygroscopic moisture. 

A more accurate determination is made by taking the 
whole of a laboratory sample, say, 1000 grammes, and drying 
it down to about 1 to 2 per cent of moisture, then crushing 
the sample, quartering and grinding and finally weighing out 
about 2 grammes for drying in an oven at 105° C. for one hour. 
The percentage moisture in the small sample is added to that 
of the large. 

Volatile Matter and Coke. — About 1 gramme of the 
powdered air-dried or partly dried coal of known moisture 
content is heated in a platinum crucible, with well-fitting lid, 
for seven minutes over a large Bunsen-burner flame. The 
burner flame should be about 8 inches high, and the crucible 
(about 30 c.c. capacity) should be 2 \ to 3J inches above the 
top of the burner. The crucible should be supported on 
a light triangle of platinum or silica. The loss of weight 
after deducting moisture represents what is known as volatile 
matter and the residue is the coke. 

The use of a Meker burner, by reason of the higher tem- 
perature, gives higher values for volatile matter than those 
ordinarily obtained, but they are not subject to so much 
variation, as the expulsion of the volatile matter is nearly 
complete. 

Ash. — Ten grammes of the powdered air-dried sample are 
placed in a shallow flat-bottomed silica dish, and heated, 
at first slowly, in a muffle-furnace until all combustible 
matter has been burnt. It is well to disturb the surface 
occasionally with a platinum or nickel wire or light silica 
rod. 

Another method is to remove the lid of the crucible after 
determining the volatile matter, burn off the carbon from 
the same, place the crucible on its side, and heat strongly 
until there is nothing but ash left. 

Sulphur. — This element, as already mentioned, exists in 
coal in at least three forms, as pyrites and as calcium sulphate, 



324 FUEL 

and as organic sulphur, the first being considered to be the 
most deleterious. 

One gramme of the finely powdered coal is mixed inti- 
mately, in a 30 c.c. platinum crucible, with about 2 grammes 
of Eschka mixture (2 parts pure calcined magnesium oxide 
and 1 part anhydrous sodium carbonate, both proved free 
from sulphate), and is covered with about half a gramme 
additional of the mixture. 

The crucible is placed in a slanting position over a Bunsen- 
burner, the mouth being shielded from the burner gases, 
which usually contain appreciable quantities of sulphur 
dioxide. 

A gentle heat is applied for about half an hour, then more 
heat is applied until the crucible becomes red-hot. The 
contents are stirred occasionally with a nickel or light silica 
rod until all the black particles disappear. On cooling, the 
crucible is washed out into a beaker ; a few c.c. of bromine 
water are added and the whole is boiled. After decantation, 
filtration, and washing, the clear liquid is acidified with 
hydrochloric acid and boiled to expel all the bromine. The 
sulphate contained therein is finally precipitated hot with 
barium chloride in the usual way. 

By placing either distilled water or solution of pure 
sodium carbonate in the bomb, in the estimation of the 
calorific value, the sulphur, which is usually completely 
oxidized to sulphuric acid, is absorbed, and can thus be 
determined conveniently and quickly. The method is 
particularly suitable for oils. 

Sulphur as Calcium Sulphate. — Weigh about 5 grammes 
of the coal, and boil for about half an hour with a 20 per 
cent solution of pure sodium carbonate ; filter. Acidify the 
filtrate with hydrochloric acid, and precipitate the sulphur 
as barium sulphate. 

Chlorine. — Mix 2 grammes of finely -powdered coal with 
about 20 grammes of pure lime free from chlorine, and burn 
in a muffle at as low a temperature as possible till the 
carbonaceous matter is all destroyed ; let cool. Dissolve 



TESTING FUELS 325 

in pure dilute nitric acid. Filter, heat to boiling, and add 
a little silver nitrate solution. Filter, wash, dry, ignite, and 
weigh the silver chloride. The weight of the silver chloride x 
•2474 will give the amount of chlorine. 

Specific Gravity. — This may be determined either by 
direct weighing or by means of the specific-gravity bottle, 
the former being the preferable method. 

1. Direct Weighing. — Remove the ordinary pan from the 
balance, attach the specific-gravity pan, and balance it. Take 
the piece of coal, which should weigh about 200-400 grains, 
attach it by a horse-hair or a piece of the finest platinum wire 
to the hook at the bottom of the pan, so that it hangs in a 
convenient position, and weigh it. This gives W, the weight 
of the sample in air. Fill a beaker of convenient size with 
water which has been recently boiled and allowed to cool, and 
which should be as nearly as possible at 60° F. (15*5° C). 
Put this under the balance-pan, so that the coal is immersed. 
Carefully remove any adherent air-bubbles by means of a 
camel's-hair brush, and weigh again. This will give W, the 
weight in water, and the specific gravity will be 

W 20 20 

fe "W _W' ' e ' 9 ' 20-4-66 15-34 6 ' 

2. The Bottle Method. — The specific-gravity bottle is a 
small flask, graduated so as to contain a known weight of 
water when quite full. The stopper is perforated so as to 
allow of the escape of excess of water without leaving an air- 
bubble. Most bottles are graduated to contain 50 grammes 
at 60° F. ; but before use each bottle should be carefully 
tested. Dry the bottle thoroughly and weigh it. Fill it up 
with recently boiled pure water at 60° F. ; wipe the outside 
quite dry and weigh it again. The increase of weight will be 
the contents of the bottle. 

Break the coal up into pieces which will go into the neck of 
the flask, and weigh about 10 grammes. Transfer the weighed 
sample to the bottle ; shake well so as to ensure removal of air- 
bubbles, or, better, put the bottle into a partially-exhausted 



326 FUEL 

receiver, or let soak for twelve hours. Then fill up the bottle 

with water, dry the outside, and weigh again. If W = weight 

of coal, B = weight of the bottle + water, B' = weight of the 

bottle + water + sample ; then W + B - B' will be the weight 

W 
of the water displaced, and ^ — ^~_1"r' ^^ ^e tne specific 

gravity. 

Analysis of Coke. — The determinations required for the 
valuation of coke are almost identically the same as those 
required for coal. The determination of volatile matter, 
especially in the case of gas-coke, should not be omitted, as it 
is sometimes appreciable in quantity. 

Porosity of Coke. — The relative amount of coke matter 
and spaces is often of importance. 

A piece of coke is selected, weighing about 40 grammes. 
This is dried in an air-bath and weighed. It is then put into 
a beaker of water, and this is gently boiled for some hours. 
The beaker is then allowed to cool, placed under the receiver 
of an air-pump and the air exhausted, this being repeated 
several times. The sample is weighed in water, then removed 
from the water, superfluous moisture wiped off, and it is 
weighed in air as quickly as possible. 

The weights obtained are : 

W = weight of dry coke. 
W = weight of dry coke in water. 
W" = weight of coke saturated with water in water. 
W" = weight of coke saturated with water in air. 

W 

Apparent specific gravity of coke =^ — ™- 

W 






True 



W-W" 



Percentage of pores =- — 7*7777 — ^77 — . 

The results obtained are only approximate. 

An approximation may also be obtained by determining 
the apparent specific gravity of the coke by weighing in air 
and water = S. 



TESTING FUELS 327 

Then determining the specific gravity of a finely -powdered 
sample of the coke in the specific -gravity bottle, which will 
give nearly the real specific gravity = S'. 

From which the relative space occupied by the pores can 
be calculated. 

Space occupied by 1 gramme of coke = ~ • 
Space occupied by 1 gramme of solid coke = qy. 

.*. Space occupied by pores = ~ -«?/ 
or percentage of the total =~ : ~ - ^: : 100 : n. 

,. (I -i-,)l00xS. 

Liquid Fuels. 

Specific Gravity. — This is very easily obtained by means of 
the specific -gravity bottle, which is filled with the liquid and 
weighed ; or by means of hydrometers, which are tubes with 
a graduated stem, loaded with mercury, the specific gravity 
being indicated by the depth to which they sink in the 
liquid. 

The Flash-point. — This can only be accurately deter- 
mined by means of apparatus specially devised for the 
purpose. It may, however, be approximately determined 
as follows : 

" Pour some of the liquid into a beaker (2 ins. x 2 ins.) to 
within about half an inch from the top ; then cover with a 
disc of asbestos, through which a thermometer passes to 
within a quarter of an inch from the bottom of the beaker. The 
beaker, etc., is now put into a sand-bath, and surrounded 
with sand to the level of the liquid. A small flame is then 
applied under the bath, and the temperature allowed to rise 
about 2° a minute. After each rise of 1° the asbestos disc is 
turned to one side, and a small flame is quickly put into the 
vapour. The temperature at which it ignites is taken as the 
flash-point.' ' * 

1 Phillips, Fuels, 17. 



328 FUEL 

Calorific Power. — This is most easily determined by means 
of the bomb calorimeter, as previously described. 

Ultimate Analysis. — The determination of carbon, hydro- 
gen, oxygen, and nitrogen can only be made satisfactorily 
by a trained chemist provided with suitable apparatus, and 
the methods used are those of ordinary organic analysis with 
which all chemists are familiar. 

The Kjeldahl method for the determination of nitrogen is 
not difficult to carry out. One gramme of the finely powdered 
coal is boiled with about 30 c.c. of sulphuric acid of highest 
concentration and half a gramme of mercury until the solution 
is nearly colourless. Oxidation is completed by adding a 
few crystals of potassium permanganate. The mercury is 
precipitated by adding potassium sulphide to the diluted 
solution, caustic soda is added in excess, and the ammonia is 
distilled over into a vessel containing 25 c.c. of normal 
sulphuric acid. The excess of acid is titrated with deci- 
normal sodium carbonate solution, using methyl orange as 
indicator. The results are not very reliable, erring on the 
low side, and the more elaborate Dumas or modified Dumas 
combustion tube method is to be preferred for accurate work. 

Gaseous Fuels. — An analysis of gaseous fuels can also 
only be satisfactorily made by a chemist by the ordinary 
methods of gas analysis. It is therefore needless to describe 
them here. 

Carbon - dioxide in Furnace Gases and Gaseous 
Fuels. — There are numerous simplified gas analysis ap- 
paratus for the determination of carbon dioxide in furnace 
gases, which is a matter of great importance. There are also 
many successful mechanisms on the market for indicating 
and recording the percentage. These are of immense service 
in fuel-saving in all kinds of furnace work, but particularly 
in boiler installations, retort houses, etc. 

One of the most successful modern instruments is known 
as the W.R.C0 2 indicator, the principle of which is shown by 
the diagram (Fig. 106a). The flue gas is aspirated through a 
filter, then through a chamber containing a porous cell in 



REFRACTORY MATERIALS 



329 



which is placed a cartridge of soda lhne for absorbing the 
C0 2 . The result is a partial vacuum within the cell. This 




Fig. 106A.— W.R.C0 2 Indicator. 



is a measure of the amount of C0 2 present, and is indicated 
on a gauge which is graduated to read percentages. 



CHAPTER XV 



REFRACTORY MATERIALS — BRICKS — CRUCIBLES 

Refractory Materials. — The materials used for build- 
ing furnaces, making crucibles, and similar purposes must be 
very refractory. A large number of refractory substances 
are found in nature, but comparatively few are of much use 
in metallurgy. Those that are used may be classified into 
groups, according to their chemical behaviour. 

1 . Acid Substances. — Those which, from the presence of a 
considerable quantity of silica, will combine readily with 
basic oxides. Among these may be mentioned : Dinas rock, 
flint, sandstones, ganister, sand, and nearly all fire-clays. 



330 FUEL 

2. Neutral Substances. — Those in which the acid and basic 
constituents are so balanced that the substance neither com- 
bines with silica nor with basic oxides, or in which the sub- 
stance itself is neither acid nor basic. The only important 
members of this group are graphite and chromite (chrome 
iron ore). Some fire-clays might be regarded as being neutral 
in composition, but almost all those used in practice are acid, 
and if measured by affinity for bases they are probably all 
best considered as acid substances. 

3. Basic Substances. — Those in which the silica is absent, 
or at any rate present in such small quantity that the basic 
power of the basic -oxides is predominant. Among these may 
be mentioned lime, dolomite or magnesium limestone, and 
magnesite. As a rule they resist the action of metallic oxides., 
but are readily attacked by silica at high temperatures. 

Fire-stones. — Many refractory rocks, usually rich in 
silica, for example, quartzites, and sandstones, such as mill- 
stone-grit, have been used in furnace construction, and re- 
fractory sandstones are now often used for the bottom of the 
hearth of blast-furnaces. The objections to the use of most 
of these materials are their liability to crack when heated, 
and the difficulty of working them into the required shapes. 
When used they should be built in the same position as 
that in which they occur, i.e. with the lines of bedding 
horizontal. 

Clay. — Clay has now become the almost universal material 
for furnace and other building, mainly on account of the ease 
with which it can be moulded into forms convenient for use. 

Clay is a hydrated silicate of alumina, and in its purest 
form constitutes the kaolin or white china clay used in the 
manufacture of pottery. This material is perfectly white, 
has a soapy feel, adheres slightly to the tongue, has the 
characteristic clay odour, and is infusible at ordinary furnace 
temperatures. Its composition is about — Alumina, 39-7 per 
cent ; silica, 46-4 per cent ; water, 13-9 per cent ; which 
corresponds to the formula, Al 2 Si 2 7 , 2H 2 0, or A1 2 3 , 2Si0 2 , 
2H 2 0. 



REFRACTORY MATERIALS 331 

Clay appears quite dry, the water present being in com- 
bination, but if more water be added it becomes plastic, and 
can be moulded into any required form. On drying it loses 
the additional hygroscopic water and with it its plasticity, 
but can be made plastic again by the addition of water. If, 
however, it be heated to redness, the water of constitution is 
expelled, and a hard mass (or biscuit) is left, which, though 
very porous and capable of absorbing a considerable quantity 
of water, cannot be made plastic again. 

Origin of Clay. — Clay is formed by the atmospheric 
decomposition of various rocks, but no doubt chiefly felspar. 
Common felspar (orthoclase) has the composition K 2 0A1 2 3 , 
6Si0 2 . When this is subjected for a long time to the action 
of air, moisture, and carbonic acid, it is broken down into a 
soft mass of china clay, all the potash and two-thirds of the 
silica being removed in solution, and water being taken up. 

If the rock were a pure felspar, a pure kaolin would result, 
but pure felspars do not often occur ; and if the rock contained 
other materials which resisted decomposition more strongly, 
these would remain with the kaolin. If, for instance, the 
rock were a granite, both silica and mica would remain mixed 
with the clay. 

Clays found in the position of the rocks from which they 
are formed, such as these pure kaolins, are comparatively rare. 
The light material produced by the decomposition of the rock 
is washed down into the sea, carried out by currents, and 
ultimately deposited somewhere on the ocean bed, necessarily 
becoming more or less mixed with impurities in the process, 
and producing therefore different varieties of clay. 

Clays belong to all geological periods. Some of the more 
recent ones are soft and plastic ; those of greater age have 
usually lost their hygroscopic water, and therefore appear 
solid and dry, but can be made plastic by the addition of 
more water ; whilst others, older still, have been subjected to 
the action of great pressure, and perhaps heat, and have passed 
into the condition of hard clay-slate, have lost their water of 
combination, and therefore the power of becoming plastic. 



332 FUEL 

Nearly all the clays that are used for metallurgical pur- 
poses occur in the coal-measures, where they often underlie 
the coal. This is so, not because equally good clays do not 
occur in other places, but because it is in the neighbourhood 
of the coal-fields that metallurgical industries are usually 
carried on and therefore that the clays are required. 

Carboniferous clays are usually dark-coloured, often black 
from the presence of organic matter. They have a talc-like 
lustre and a soapy feel, adhere strongly to the tongue, have 
a hardness of about 1-5, and therefore can be scratched readily 
with the nail. They can be easily powdered, and on mixing 
with water yield a stiff plastic mass. This power of becoming 
plastic with water is the characteristic of a clay. When these 
clays are fired they become white, the organic matter being 
completely burned away. 

Fire-clays. — Pure kaolin is very difficult to fuse, the 
silica and alumina being present almost exactly in proportions 
which give great infusibility, but the presence of impurities, 
even in very small quantities, may increase the fusibility very 
much. Those clays which are free from such impurities, and 
therefore can be used for making fire-bricks or other articles 
which have to stand a high temperature, are called fire- 
clays. 

Almost all fire-clays contain more silica than pure kaolin, 
and therefore may be considered as siliceous or acid clays. 
Stourbridge clay, for instance, contains about 63 per cent of 
silica. As a typical analysis of Stourbridge clay the following 
figures may be taken : 

Silica 63-30 

Alumina 23-30 

Lime ....... -73 

Ferrous oxide . . . . .1-80 

Moisture and organic matter . .10-30 

99-43 

Calculating out the percentage of pure clay from these figures 
the analysis would become : 



REFRACTORY MATERIALS 



333 



Clay, A1 2 3 , 2Si0 2 , 2H 2 . 

Silica in excess of that in clay . . 

Impurities ........ 

Water in excess of that in the clay and organic matter 



58-90 

36-10 

2-53 

1-90 

99-43 



The addition of silica to a fire-clay does not necessarily 
increase the refractoriness, in fact as a rule, depending on the 
nature of the silica, an increase causes a reduction in the 
refractoriness up to a certain point. 

Examples of Fire-clays. — The following analyses will 
serve to illustrate the composition of fire-clays : 





1. 
55-61 


2. 


3. 


4. 


5. 


6. 


7. 


8. 


Silica .... 


56-42 


58-00 


62-35 


44-37 


6510 


48-04 


48-99 


Alumina 


27-50 


26-35 


30-85 


18-47 


38-59 


22-22 


34-47 


3211 


Oxide of iron 


1-91 


1-33 


1-55 


4-77 


1-82 


1-92 


305 


2-34 


Lime .... 


•32 


•60 


•80 


trace 


•51 


•14 


•66 


•43 


Magnesia 


•79 


•55 




1-36 


•30 


•18 


•45 


•22 


Potash .... 


•81 


•48 




2 47 




•18 


1-94 


3-31 


Soda .... 


















Titanic acid . 


•33 


115 




110 










Organic matter or loss \ 
in calcinate / 


3-34 






\ 




•58^ 






" I 


9-70 


5-22 j 


11-78 


11-15 


9-63 


Combined water . 


9-96 


10-95 f 




710 f 

2-18J 






Moisture 


2-12 


2-80J 




415 


2-69 




2-33 


99-69 


100-63 




99-89 


99-99 









1. Etherley (Riley). 2, Glenboig (Riley). 3, French Normandy, best (Greiner). 
4, Derbyshire (Riley). 5, Garnkirk (Wallace). 6, Stourbridge, used for glass pots 
(Percy). 7, Stannington (Percy). 8, Poole, used for Cornish crucibles (Percy). 

Impurities in Fire-clay. — There are several impurities 
almost always present, as will be seen from the analyses, and 
some of these have a deleterious effect on the refractoriness of 
the clay. 

Alkalies. — These are always present, though sometimes 
they are not determined and therefore are not shown in the 
analyses ; but as a rule an analysis of a clay that does not 
give the alkalies is worse than useless. Snelus * states that 
1 per cent of alkalies renders a clay too fusible to be used for 
purposes where high temperatures are required. There is, 
however, no doubt that many fire-clays in actual use contain 
more than this, and sometimes considerably so. 

Lime and Magnesia. — These also have a fluxing effect, and 

1 J.I. and S.I., 1875, ii. p. 5^3, 



334; FUEL 

should not be present in large quantity ; it is, however, 
impossible to fix an actual limit. 

Oxide of Iron. — The behaviour of oxide of iron is some- 
what peculiar. Undoubtedly the less oxide of iron present 
the better, since it can do no good. It will be seen that some 
of the clays given in the table contain a very considerable 
quantity of oxide of iron. Snelus says that it may be present 
up to 2 or 3 per cent without affecting the fusibility of the 
bricks in a very serious degree, provided that only a small 
amount of alkalies is present. 

The differences in the statements that have been made as 
to the effect of iron on the refractoriness of fire-clays have 
probably arisen from the fact, that it varies with the form in 
which the iron is present and the conditions under which the 
brick is to be used. If the iron be diffused through the clay 
in the form of oxide, it will impart a reddish colour to the 
brick when it is burned. Such a brick, provided the amount 
of iron be not too large, may be very refractory if heated in an 
oxidizing atmosphere, because ferric oxide (Fe 2 3 ) and silica 
do not combine, but if it be heated in a reducing atmosphere 
the ferric oxide will be reduced to ferrous oxide, which will 
combine with the silica and form fusible ferrous silicate, thus 
destroying the brick. Such a brick therefore would be quite 
useless for lining a blast-furnace, but might stand well in a 
reverberatory roasting furnace. The iron may, however, be 
present in the form of minute specks of pyrites scattered 
through the clay ; its action will then be different, and either 
more or less injurious according to the purpose for which 
the brick is to be used. When the brick is fired the sulphur 
of the pyrites burns out thus, FeS 2 + 50 =FeO + 2S0 2 , and the 
ferrous oxide at once combines with some of the silica, form- 
ing ferrous silicate, which, being liquid, is at once absorbed by 
the brick ; thus, where the speck of pyrites was, a small hole 
is left, surrounded by a black stain of ferrous silicate. The 
ferrous silicate present in this form does not seem to seriously 
impair the fire-resisting power of the brick. 

Alumina. — If in large quantity this gives the clay great 



REFRACTORY MATERIALS 



335 



plasticity, and a soapy feel, and makes it shrink very much on 
drying and firing, but such bricks afterwards undergo little 
change by heating or cooling. Alumina itself is very highly 
refractory. 

Titanic Oxide, Ti0 2 , is very frequently present in clay, but 
does not seem to have any injurious effect. 

Combined Effect of Impurities. — Bischof measures 
the refractoriness of a clay by what he calls the refractory 
quotient, which he obtains by dividing the quotient of the 
oxygen of the fluxes into that of the alumina by the quotient 
of the oxygen of the alumina into that of the silica, i.e. 
O in ALO, . O in Si0 2 



l 2^3 



in RO ' O in A1 2 3 

In Bischof s standard fire-clays the coefficient is 13-95 in 
the most refractory and 1-64 in the least refractory. 1 The 
amount of fluxing impurities, i.e. RO oxides, must not exceed 
6 per cent. 

Ganister. — With the introduction of the Bessemer process 
it became necessary to find a very refractory substance with 
which to line converters, and ganister was the material 
selected, and it is still very largely used. The ganister is an 
argillaceous sandstone occurring in the carboniferous series of 
various parts of the country, the best known being that which 
occurs near Sheffield, and is known as Lowood's Sheffield 
ganister. The following analyses will show its nature : 





1. 


2. 


3. 


4. 


5. 


Silica 


98-94 


89-37 


88-36 


97-78 


89-04 


Alumina .... 


•57 


6-36 


7-00 


•20 


5-44 


Oxide of iron. 


•67 


1-73 


2-00 


•21 


2-65 


Lime 


•62 


•70 


•22 


•38 


•31 


Magnesia .... 


•21 


•36 


•15 


•44 


•17 


Alkalies 


. . 






•26 




Water, or loss on calcination 


•42 


2-88 


2-32 


•73 


2-30 


101-43 


101-40 


100-05 


100-00 


99-91 



1, Hard (Riley). 2, Soft (Riley). 3, Lowood (Snelus). 4, Scotch, Bonnymuir. 5, Lowood. 

, x See Hofman and Demond, " Refractoriness of Fire-clays," J.A.I.M.E., 
xxiv. 



336 



FUEL 



The nature of such a material is easily seen. Assuming 
the formula for clay already given, analysis 5 works out : 



Silica (in excess of that in clay) 

Clay 

Impurities . . . . 

Moisture, etc. 



81-28 

15-30 

313 

•20 

99-91 



It is therefore a siliceous material with just enough clay to 
make it bind, and when fired it yields a strong brick. Ganister 
bricks, owing to their very refractory nature and their much 
greater strength than silica bricks, are very largely used. 

Ganister is properly the name of a special rock, but any 
similar material is called by the same name, and some ganister 
bricks are made of a mixture of a more siliceous material and 
clay. 

Siliceous Materials. — Materials containing more silica 
are used for the manufacture of silica bricks and other pur- 
poses. When used for brick-making, they must be mixed 
with some binding material, as they have no cohesive power 
of themselves. Among the materials used may be mentioned 
Dinas rock, calcined flints, white sand, etc. White sand is 
used for the final layer in lining the Siemens steel furnaces, 
and less refractory sands containing iron are used for the under 
layers. 

Siliceous Refractory Materials 





1. 


2. 


3. 


4. 


Silica .... 


98-31 


96-73 


9313 


96-7 


Alumina .... 


•72 


1-39 


4-30 


}i. 


Oxide of iron 


•18 


•48 


•29 


Lime .... 


•22 


•19 






Alkalies .... 


•14 


•20 


•74 




Water .... 


•35 


•50 


1-55 


20 



1 and 2, Dinas rock (W. Weston). 3, Sand for Siemens furnaces. 4, White sand. 



Neutral Refractory Materials 

Graphite.— Graphite is almost pure carbon ; it is one of 
the few substances that have never been fused. It is black in 



REFRACTORY MATERIALS 



337 



colour with a metallic lustre ; its hardness is about 1, it marks 
paper readily, and burns at a high temperature leaving a 
residue of ash. It is not plastic, and the powder does not 
adhere even on strong firing, so that if it is to be used for 
making crucibles, it must be mixed with clay or similar 
materials. Being quite neutral, it is sometimes used as a 
separating layer between the acid and basic portions of basic 
open-hearth furnaces. 

Analysis of Graphites. 





1. 


2. 


3. 


4. 


5. 


Volatile matter . 
Carbon .... 
Ash ... . 
Specific gravity . 


110 

91-55 
7-35 
2-3455 


1-82 
78-48 
19-70 

2-2863 


510 
79-40 
15-50 

2-3501 


•158 
99-792 
•050 
2-2671 


•7 
66-4 
32-9 



1, Cumberland. 2, Canada. 3, Ceylon (these are by Mene, quoted from Percy). 
4, Ceylon (Ferguson). 5, Austrian. 

Carbon in the form of gas-retort carbon is sometimes used 
for crucibles, etc. 

Chromite. — This material, which is a double oxide of iron 
and chromium, having the formula Cr 2 3 FeO, has often been 
suggested as a neutral lining for steel and other furnaces 
where the lining is required to stand a very high temperature. 
Norwegian chromite, which has been principally used, occurs 
with a gangue of serpentine, and this mixture is excessively 
infusible. The chrome ore has also been made into bricks 
by crushing, mixing with lime, and firing. The following 
analyses are of good chromite. There should be more than 
40 per cent of chromic oxide, and less than 6 per cent of 
silica. Chromite is not acted on by siliceous fluxes. 





1. 


2. 


Chromic oxide . 


51-23 


62-20 


Ferrous oxide 


36-63 


2810 


Alumina .... 


317 


2-60 


Magnesia .... 


3-79 


110 


Lime 


510 


3-07 


Silica 


1-87 


2-60 



( D 107 ) 



338 



FUEL 



Basic Materials. — The introduction of the basic 
Bessemer and basic open-hearth steel processes led to a 
demand for basic materials, which could be used for lining 
furnaces or for making into bricks, and several such sub- 
stances are now in use. 

Lime. — Lime (CaO) is an extremely refractory substance, 
never having been fused or even softened, and, of course, it is 
basic ; but there have been difficulties in using it which have 
prevented it coming largely into use, though it was the first 
material to be suggested for lining basic converters. The 
objections to it are that it is extremely difficult to get it to 
bind, a small quantity of silica not having the same fritting 
effect with it that it has with some other basic materials. It 
is used to some extent for fining basic converters, as, though 
inferior to dolomite for the purpose it is much cheaper. 

Magnesian Limestone. — The suitability of this material 
for lining basic Bessemer converters was discovered by Messrs. 
Thomas and Gilchrist, and at once made the process now 
known by their names a success. The material occurs in the 
trias beds of the north of England, and is usually, though im- 
properly, called dolomite. Dolomite is a definite mineral, Ca 
C0 3 , MgC0 3 , containing the carbonates of lime and magnesia 
in nearly equivalent proportions. The magnesian limestone 
is of uncertain composition, containing varying proportions 
of the two carbonates with a small and varying quantity of 
silica, which is essential to it for this purpose. 

The following analyses of dolomite used for basic linings 
will be sufficient to indicate its character : 





1. 


2. 


3. 


4. 


5. 


Lime 

Magnesia .... 

Silica 

Alumina 

Oxide of iron 

Carbon dioxide 

Water 


31-62 
20-19 

1-70 
•09 

1-22 
45-35 


29-86 

20-17 

4-34 

45-64J 


28-3 

18-6 
410 
3-00) 
1-70/ 

44-2 


28-0 
17-0 
3-80 

4-00 
45-00 


28-0 
17-0 
2-08 

2-57 

45 00 



1 and 2, Wedding, localities not given. 3, Vairgey, France. 
5, Horde, Germany. 3, 4, and 5, by Zyromski. 



4, Besseges, France. 



REFRACTOEY MATERIALS 



339 



The more magnesia a dolomite contains the better. 
Zyromski believes that, other things being equal, the best 
dolomite for open-hearth furnaces should contain over 20 per 
cent of magnesia. Such a dolomite agglomerates well, hardens 
rapidly, and is still very refractory. The calcination is more 
complete and easier, the nearer a total of 4 per cent is reached 
for ferric oxide and alumina. 

Magnesite. — This is probably the most valuable of all the 
basic materials. When calcined at a very high temperature 
it loses carbon dioxide, and the residue left is absolutely 
infusible at furnace temperatures ; it is usually dark brown 
from the presence of oxide of iron ; it agglomerates very 
little, far less than dolomite, and though necessarily very 
basic, it does not combine with silica when the two are heated 
in contact, so that when it is used in a steel furnace, the basic 
lining and acid walls may come in contact without danger. 
The only objection to magnesite is its expense, there being 
but few localities where it occurs. The best known, and 
probably the best for Bessemer converters, is the Styrian 
(especially that of Veitsch) . Furnaces lined with this material 
are far more durable than those lined with dolomite. 

The following analyses will show the nature of the 
material : 





1. 


2. 


3. 


Lime 




1-50 


1-68 


1-72 


Magnesia 




47-00 


42-43 


44-06 


Silica 




•50 


•92 


1-93 


Iron oxide 
Alumina 




•• \ 


4-30 


/ 3-56 
I '31 


Carbon dioxide 
Water 


} 


51 


50-41 


48-02 



1, Euboea, Greece. 



2, Mittendorf, Styria. (1 and 2, by Zyromski.) 
3, Veitsch, Styria. 



Bauxite. — This abundant mineral is a hydrated double 
oxide of iron and alumina in very varying proportions — 
zAl 2 3 , 2/Fe 2 3 , 3 H 2 0, the quantity of iron being small in 
bauxite, but increasing as the mineral passes gradually into 



340 FUEL 

aluminous iron ore, in which the iron is present in large 
quantity. It is usually yellow in colour, owing to the pre- 
sence of oxide or iron, though pure white varieties occur 
which are almost free from iron. Bauxite for brick-making 
should contain but little iron or silica. A sample said to be 
suitable for brick-making contained — Alumina, 90 per cent ; 
titanic acid, 5 per cent ; silica, 2 per cent ; oxide of iron, 1 
per cent ; lime, 1*5 to 2 per cent. 

Other Refractory Materials 

Bull-dog. — This is a mixture of ferric oxide and silica 
made by roasting tap cinder with free access of air. Tap 
cinder is a basic silicate of iron — 2 FeO, Si0 2 , approximately, 
and on roasting it takes up oxygen, and gives a mixture of 
ferric oxide and silica. As these do not unite, the substance 
is infusible in an oxidizing atmosphere, but fuses in a re- 
ducing atmosphere, ferrous silicate being re-formed. 

Iron Ores. — Some of these, especially haematite (Fe 2 3 ), 
magnetite (Fe 3 4 ), burnt ore and Blue Billy (artificial Fe 2 3 ), 
are occasionally used for furnace linings. 

Fire-bricks. — These are bricks used for furnace construc- 
tion or other purposes where a high temperature is required. 
They may be made of any of the refractory materials 
described. 

The qualities required in good fire-bricks are as follows : 

" They should not melt or soften in a sensible degree by 
exposure to intense heat long and uninterruptedly continued. 

" They should resist sudden and great extremes of tem- 
perature. 

" They should support considerable pressure at high tem- 
peratures without crumbling. 

" They may be required to withstand as far as practicable 
the corrosive action of slags rich in protoxide of iron or other 
metallic oxides." * 

These qualities are not all shown in the highest degree 

* Percy, Fuel, p. 144. 






BRICKS 341 

by any one brick. In selecting a brick, therefore, attention 
must always be given to the conditions in which it will be 
placed, for one which would be good under one set of con- 
ditions may prove very bad under another. 

Fire-clay Bricks. — These are the most generally used of 
all the refractory bricks. They are refractory enough for 
most purposes, and the plasticity of the clay allows of their 
being easily made of any required form or size. 

Fire-bricks should be nearly white in colour, any tinge 
of red indicating an excess of iron ; and should be as free as 
possible from small holes surrounded by black spots, though 
for most purposes these do not seem to be very injurious. 
Fire-clay bricks shrink very much on drying and firing. 
At St. Helens, "for a 9 x 4 J x 2|-inch brick the mould is 
9f x 4| x 3 J inches. For Glenboig clay a shrinkage of -^ is 
allowed ; that is, the mould for a 9-inch brick is made 
9| inches long." x 

Each clay has its own rate of contraction, which can only 
be learned by experience. Though clay bricks shrink so 
much in the firing, once finished they alter very little with 
changes of temperature. The more aluminous bricks seem 
to expand and contract less than the more siliceous, and 
therefore such bricks as Glenboig bricks are largely used for 
regenerators and other positions where change of form would 
lead to inconvenience. 

Manufacture of Fire-clay Bricks. — The methods for 
the manufacture of fire-bricks are the same in principle, but 
differ in detail in different works. 

The following is an outline of the process as conducted 
in a large Scotch fire-brick works : 

The clay as raised from the mine is perfectly dry, and is at 
once put into a mill, where it is ground to a coarse powder. 
It then passes through a sieve, any not sufficiently finely 
ground being returned to the mill. After this dry grinding 
the powder is transferred to a pug-mill, and is thoroughly 
incorporated with the necessary amount of water to give it 

1 Snelus. 



342 FUEL 

the required consistency. If large slabs are to be made, 
some ground burned clay is added, but this is not necessary 
for ordinary-sized bricks. The paste is raised by an elevator 
to a higher floor, where it is distributed by barrows to shoots, 
by which it passes down to the work benches. On each 
bench is fixed a plate to form the bottom of the brick mould. 
This is covered with felt, through which projects the brass 
die to form the name or other mark on the brick. On this 
plate is placed a rectangular bronze mould, the size required 
for the bricks being made. The workman cuts a piece of the 
stiff clay off the mass descending on to the bench from the 
shoot above, puts it into the mould, presses it firmly down, 
cuts off excess of clay from the top by means of a smoothing - 
board, and the boy in attendance at once carries the brick 
away, and sets it on edge on the drying-floor. A work- 
man and boy can make about 2000 bricks a day by this 
process. 

The drying-floor is of iron, heated by fireplaces and cir- 
culating flues, the floor immediately over the fires being 
protected by means of a curtain arch. The drying takes 24 
hours, and the bricks are then ready for firing. 

Many attempts have been made to introduce machinery 
for fire-brick making, but up to the present without great 
success. 

The bricks are, after drying, fired in kilns. The ordinary 
kiln consists of a large chamber capable of holding 25,000 
bricks, provided with a series of deep fireplaces, so deep as 
to be almost called gas-producers, on each side. The bricks 
are stacked in the kilns, the fires lighted, ample air being 
admitted to ensure the combustion of the products of distil- 
lation, and the products of combustion circulate through the 
loosely-stacked bricks on their way to the chimney. Such 
a kiln will take about ten days to work a heat — three days 
heating up, three days firing, and four days cooling. 

At the Glenboig works Mr. Dunnachie's regenerative 
gas-kiln is used with great success. These kilns are built in 
sets of ten, in two rows of five each. The gas is supplied by 



BRICKS 



343 



Wilson producers, and is so arranged that it can be sent 
through the chambers in any order. The gas enters the kiln 
by a flue running along the bottom on one side, the hot air 
is supplied just above it, and combustion takes place. The 
products of combustion sweep across the kiln through the 
bricks stacked in it, and leave at the other side. When at 
work there will be two kilns cooling off, the air passing 
through these on its way to the kiln where burning is going 



££/^£e£f. 




FIG. 107. — Dunnachie's Patent Regenerative Gas-kiln. 



on, and being heated on the way by the hot bricks ; the hot 
products of combustion pass through two or three more kilns 
which are filled with unburned bricks, and which are there- 
fore being heated up, and other kilns are being charged and 
discharged. As soon as the burning is complete the valves 
are adjusted, so that the second of the two cooling-off ovens 
is ready for discharging, the finished oven begins to cool off, 
and the oven which was being charged last begins to dry. 
In the illustration, Nos. 10 and 1 are cooling off ; 2 is burning ; 
3, 4, 5, and 6 are in different stages of heating up and drying ; 
*7, 8, 9 are being charged or emptied. This kiln is worked 



344 FUEL 

continuously, and is found to be very convenient and 
economical. 

Ganister Bricks. — These are made in much the same 
way, but are very tender before firing, and therefore require 
careful handling. The clay present in the ganister is enough 
to act as a binding material. 

Silica Bricks. — Since silica has no binding power, it is 
necessary to add some material which will bind the silica 
together. A small quantity of clay has been used, but the 
usual agent is lime, a small quantity (about 1 per cent) of 
which is mixed with the material ; on firing, this attacks the 
silica, forming a frit which binds the brick together. Silica 
bricks are weak and friable, but are capable of withstanding 
very high temperatures. Silica bricks expand on burning, 
so that the moulds have to be made a little smaller than the 
required brick. Silica bricks also expand and contract very 
much when subject to heat, and when steel-furnace roofs 
are built of them, care has to be taken to loosen the tie-rods 
of the furnace to allow for the expansion. 

Manufacture of Silica Bricks. — The manufacture of 
Dinas bricks is described by Dr. Percy. 1 " The rock when 
not too hard is crushed to coarse powder between iron rolls. 
By exposure to the air the hard rock becomes somewhat 
softer, but some of it is so hard that it cannot be profitably 
employed." " The powder of the rock is mixed with about 
1 per cent of lime and sufficient water to make it cohere 
slightly by pressure. This mixture is pressed into iron 
moulds, of which two are fixed under one press side by side. 
The mould, which is open top and bottom like ordinary 
brick moulds, is closed below by a movable iron plate, and 
above by another plate of iron which fits like a piston, and is 
connected with a lever. The machine being adjusted, the 
coarse mixture is put into the moulds by workmen whose 
hands are protected by stout gloves, as the sharp edges of 
the fragments would otherwise wound them ; the piston is 
then pressed down, after which the bottom plate of iron on 

1 Fuel, p. 147. 



BRICKS 



345 



which the brick is formed is lowered and taken away with 
the brick upon it, as it is not sufficiently solid to admit of 
being carried in the usual manner. The bricks are dried on 
these plates upon floors warmed by flues passing under- 
neath, and when dry they are piled in a circular closed kiln 
covered with a dome similar to kilns in which common fire- 
bricks are burned. About seven days' hard firing are 
required for these bricks, and about the same time for 




FIG. 108.— Basic Brick Press. 



cooling the kiln. One kiln contains 32,000 bricks, and con- 
sumes 40 tons of coal, half free-burning half -binding." 

Silica bricks may be made by exactly similar methods 
from any siliceous material, ground flints, sand, and other 
similar materials being frequently used. 

Basic Bricks. — For fining basic Bessemer converters and 
other purposes dolomite bricks are made. The dolomite is 
calcined so as to expel all carbon dioxide, a much higher tem- 
perature being required than for calcining limestone. The 



346 FUEL 

more magnesia present the higher the temperature required, 
but the less the substance deteriorates on exposure to the air. 
The calcined material is ground, mixed to a stiff paste with hot 
anhydrous tar, and the mixture is moulded into bricks under 
hydraulic pressure in iron moulds ; the bricks are then care- 
fully dried and fired at a high temperature. The brick 
press shown has three moulds on a rotating table, and when 
one mould is under the pressing ram, another is being filled, 
and the brick is being removed from the third. 

Magnesite is more difficult to calcine than dolomite, and 
must be calcined at an intense white heat. It is then ground, 
made into bricks in the usual way, dried, and fired at a 
very high temperature, the iron oxide present acting as a 
frit. These bricks are dark chocolate in colour, are strong, 
and have a very high specific gravity. Burned magnesite 
may be exposed to the air without fear of its absorbing water 
or carbon dioxide. Bauxite bricks are made by mixing the 
calcined mineral with enough clay to make it bind. These 
bricks are dense, but are usually friable. 

Furnace Linings. — Some refractory materials are used 
for the linings of converters or furnaces directly without 
being made into bricks. 

Ganister is used for lining converters for the ordinary or 
acid Bessemer process. The ground material is mixed to a 
paste with water, and is applied to the interior in several 
ways. The usual way, probably, is to put inside the con- 
verter a core of the shape it is intended to make the inside, 
and then to ram the ganister between this and the shell. 
Another method is to apply the well-worked ganister by 
hand, pressing it firmly against the inside of the shell, and 
when all is in, carefully smoothing the interior surface. 

Dolomite is used for lining converters for the basic 
Bessemer process. When not used in the form of bricks, 
the hot mixture of dolomite and tar is rammed into place 
round a core by means of a hot iron rammer. 

For the hearth of basic open-hearth furnaces, the mag- 
nesian lime is spread in thin layers, each of which is fritted 



BRICKS 



347 



by the heat of the fire before another is put in. Magnesite 
is used similarly. 

Sand. — This is used for making the hearths of Siemens 
furnaces. Several qualities are used, and they are spread in 
thin layers, the least refractory first, the most refractory last, 
each layer being fritted before another is applied. Bull-dog, 
iron-ore slag, and other materials used for furnace lining 
are similarly applied. 

Mortars, etc. — In setting bricks of any kind that are to 
be exposed to a high temperature, care must be taken to use 
a mortar which has no action on them. Acid bricks must be 
set with an acid mortar, and basic bricks with a basic one. 
Fire-bricks are usually set in fire-clay, dolomite bricks in a 
dolomite tar mortar, and others in a material as nearly as 
possible the same composition as the bricks themselves. 

Casting Sands. — These sands, used for making moulds 
for casting purposes, are not very refractory, as they must 
contain enough alumina to make them bind. The following 
examples are from Percy : x 





1. 


2. 


3. 


4. 


5. 


Silica 


79-02 


92-083 


91-907 


92-913 


87-87 


Alumina .... 


13-72 


5-415 


5-683 


5-850 


213 


Oxide of iron 


2-40 


2-498 


2-177 


1-249 


2-72 


Magnesia .... 


•71 






. . 


•21 


Lime ..... 




trace 


•415 


trace 


3-79 


Alkalies .... 


4-53 










Carbonic acid and water . 






'• 




2-60 


100-38 


99-996 


100182 


100-012 


99-32 



1, Ibsenberg. 2, Charlottenberg Foundry. 3, Used in Paris for bronzes. 4, Sand 
from Manchester. 5, Sand used for bed of copper furnace (Weston). 

" According to Kaufman a good sand for moulds may be 
artificially made from the following mixture : 

Fine quartzose sand ....... 93 

Red English ochre ....... 2 

Aluminous earth, as little calcareous as possible . . 5 

100" 2 



1 Percy, Fuel, p. 151. 



2 Fuel, p. 152. 



348 FUEL 

Crucibles. — Crucibles are open-topped vessels in which 
materials may be heated in furnaces, and of such a size that 
they can be lifted by means of tongs. 

The qualities required in good crucibles may be thus 
enumerated : 

" 1. They should resist a high temperature without 
melting or softening in a sensible degree, and should not be 
so tender while hot as to be liable to crumble or break when 
grasped with the tongs. 

" 2. In some cases they should resist sudden and great 
changes of temperature, so that they may be plunged while 
cold into a nearly white-hot furnace without cracking ; 
while in other cases it is only necessary that they should 
resist a high temperature after having been gradually heated. 

" They may occasionally be required to withstand the 
corrosive action and permeation by such matters as molten 
oxide of lead. 

" In special cases the material of which they are com- 
posed must not contain any ingredient that would act 
chemically upon the substances heated in them. Thus 
carbonaceous matter should not be one of their constituents 
when they are used in the heating of such oxidized matters, 
as carbon would reduce, and reduction is not desired, or in 
the fusion of steel, when it is necessary that the proportion 
of carbon should not be increased." 1 

Clay Crucibles. — Various forms of crucibles are in use. 
At one time each form of crucible was made in some special 
locality, and of some special mixture of clays. That, how- 
ever, is no longer the case. Crucibles of good quality can be 
obtained of any required forms. 

Among the best-known forms of crucibles may be men- 
tioned the following, made by the Morgan Crucible Company, 
Battersea : 

Cornish Crucibles. — These crucibles were made by Messrs. 
Juleff of Redruth for copper assaying, and acquired a great 
reputation, and they are now made from Juleff's formula by 

1 Percy, Fuel, p. 110. 






CRUCIBLES 349 

the Morgan Crucible Company. They are round, and of two 
sizes, the larger 3 inches in diameter at the top, and 3J 
inches high, the smaller fitting into this. 

They are nearly white in colour, spotted with brown spots. 
They are not very refractory, but Percy states that they 
can be plunged into a white-hot furnace without cracking, 



^Q— -> Londoix SS? Loixdoix 

Round f^lfe Triarj 






It 



w 




JkCttU Pot For Copper 

Fig. 109.— Forms of Crucibles. 

and will therefore stand sudden and violent alternations of 
temperature. 

Percy gives the following as an analysis of a good batch of 
these crucibles : 

Silica 72-39 

Alumina 25-32 

Sesquioxide of iron .... 1-07 

Lime ....... -38 

Potash 1-14 

100-30 

For more refractory crucibles of small size a little china clay 
is added to the mixture. 

London Crucibles. — This is a deeper form of crucible than 
the Cornish. The original London crucibles are stated by 
Percy to be very liable to crack. 

Batter sea-round. — These crucibles are very excellent for 
all ordinary laboratory purposes. They stand all assay 



350 FUEL 

furnace temperatures quite well, and are not liable to 
crack. 

Hessian Crucibles. — These crucibles at one time had a 
high reputation, but are little used now. The name is 
retained to indicate crucibles which have a triangular top, 
quite irrespective of the materials of which they are made. 

Among other types of small crucibles may be mentioned 
German assay crucibles, skittle-pots, gold annealing pots, etc. 

Selection of Materials for Crucible - making. — The 
clay for making crucibles, whether large or small, must be 
very carefully selected. It must be very plastic so as to 
allow of ready moulding into the required form, and it is said 
to be best after weathering. It must be infusible, and must 
not contain iron pyrites, or the holes left by its decomposi- 
tion may form channels through which the contents of the 
crucible might escape. Clay contracts so much on drying 
and firing that a crucible made of raw clay only would lose 
its shape. To overcome this defect the clay is always mixed 
with some non-contracting and infusible material, such as 
burned clay, silica, or graphite. Burned clay is the material 
generally used ; but care must be taken not to add so much 
as to reduce the plasticity of the clay. The material must 
not be too finely powdered, as the more finely divided it is 
the more likely it is to fuse. Berthier states that if silica be 
used it may at a high temperature combine with the clay, 
forming a pasty mass. 

Manufacture of Crucibles. — Crucibles are articles of 
pottery, and therefore they may be made by the usual 
methods for the manufacture of such ware. The methods 
of making Stourbridge-clay crucibles is thus described by 
Percy: 1 " The workman sits before a bench, on which is a 
wooden block, of the shape of the cavity of the crucible. At 
the widest end of the block is a flange or projecting border, 
equal in width to the thickness of the crucible at the mouth, 
measured in the wet state. At the middle of the same end 
an iron spindle is inserted, which fits into a socket on the 

1 Fuel, p. 116. 



CRUCIBLES 351 

bench. The block may thus be made to revolve. It is not 
fixed, but may be taken out or dropped into the socket at 
pleasure. On the narrow or upper end of the block is placed 
a lump of tempered clay, which the workman then moulds 
round the block by first striking it with a flat piece of wood, 
and then slapping it with both hands so as to turn the block 
more or less each time as occasion may require. The clay 
is thus rapidly extended over the whole block down to the 
flange. A sliding vertical gauge is fixed in the bench, by 
means of which the thickness of the sides and bottom of the 
crucible may be regulated. As soon as the moulding is 
finished the block is lifted out of its socket and inverted, 
when the crucible, with a little easing, will gently drop off. 
The spout for pouring out metal is then fashioned with the 
finger. The clay may likewise be moulded upon a linen cap, 
wetted, and slipped over the block, so that on inverting the 
block the crucible and cap slide off together, after which the 
cap may be pulled out when the crucible is dry." After 
this they are very carefully dried and fired. 

Manufacture of Crucibles for Steel-melting. — The 
materials (each maker having his own mixture of clays) 
are thoroughly mixed with water, and tempered by mixing 
in a mill or by treading with bare feet for several hours, 
cutting and turning at intervals with the spade. The mass 
is then cut up into balls, each containing about enough for 
one crucible. The ball is placed in a " flask," the interior of 
which is the form of the outside of the crucible. A plug 
having the form of the interior of the crucible, with a spike 
which fits into a hole in the base-plate, is pressed down, 
then forced down by being lifted and let fall, and finally 
driven home by a hammer. The clay rises up in the space 
between the flask and the core. That which projects above 
is cut off neatly, the crucible is forced out of the flask and put 
to dry, after which it is used without firing, being placed on 
a brick sprinkled with sand, to which it adheres as soon as 
its temperature is high enough, and thus prevents any 
escape of metal. 



352 FUEL 

Machines are now sometimes used. In these the core is 
forced down by machinery, and the centring-pin is dispensed 
with. 

Small Crucibles for Laboratory Use. — These are 
made in a small brass flask by means of a wooden core. The 
brass flask A (Fig. 110) is fitted into a wooden base c, in the 
centre of which is a small hole, into which the centring-pin 
G of the core fits. A quantity of a well-kneaded mixture of 
clay and burned clay, enough to make a crucible, is put into 
the mould, the core f is pressed down, a rotary motion being 
given it, so as to force up the clay between it and the flask, 

till the neck of the core comes down 
on to the top of the flask, any excess 
of clay being forced out of an open- 
ing left in the head of the core. The 
core is then removed, a small piece of 
clay dropped in to stop the hole in 
the bottom, and the interior is 
smoothed off by means of an exactly 
similar core, without the pin. The 
crucible is then removed by lifting 
the flask from the stand, and apply- 

Laboratory Crucible-making m g slight pressure below. In Order 
Apparatus. , . 

to prevent sticking, it is well to 
oil the flask and the cores. 

Every chemist is familiar with the high quality of Royal 
Berlin or Dresden porcelain, and its suitability for laboratory 
crucibles, basins, etc. It is manufactured from the best 
china clay, properly weathered, aged and worked up under 
scientifically supervised conditions. It is only thus that 
these articles can be guaranteed to withstand the highest 
temperatures and great fluctuations of temperature. 

Plumbago or Black-lead Crucibles. — These crucibles are 
made of a mixture of fire-clay and graphite, the graphite 
preventing shrinking, and at the same time adding very 
much to the refractoriness of the pot. Black-lead pots are 
very much more durable than fire-clay crucibles, and can be 




CRUCIBLES 



353 



used several times, whilst clay crucibles can usually only be 
used once. They are also much less likely to crack in the 
furnace. 

Manufacture of Plumbago Crucibles at Messrs. Mor- 
gan's. — A weighed portion of the mixture of clay and 
graphite in the plastic condition is introduced into an iron 
flask f (Fig. Ill), which is so fixed that it can be rotated by 
machinery. A forming-tool or template of iron m, having 
the form of the interior of the 
crucible, is lowered into the 
flask till it just touches the ball 
of graphite and clay c, and the 
flask is rotated, the "former" 
being gradually lowered till the 
crucible is complete. Any excess 
of material is then cut off, the 
crucible is lifted out, the spout 
formed with the finger, and the 
mould, with the crucible in it, is 
set aside to dry. In drying, the 
crucible contracts and separates 
from the mould. When dry 
enough it is fired. 

A crucible examined by Dr. 
Percy was found to contain 48*34 
per cent of carbon. 

Manufacture of Black-lead 
Crucibles in America. 1 — The mixtures used consist of about 
50 per cent graphite, 45 per cent air-dried clay, and 5 per 
cent sand, and lose on burning from 5 to 10 per cent. Ceylon 
graphite is generally used. This is very pure, containing not 
more than 5 per cent of ash. The graphite is crushed in 
mills, pulverized between millstones, and passed through a 
40 sieve. 

" If the graphite be too coarse, the crucible is apt to 
become porous, and to be weakened by cleavage planes ; 

1 Abridged from account by Howe in The Metallurgy of Steel, p. 299. 
(DJ07) 2A 




Fig. hi. 

Apparatus for making Black-lead 

Crucibles. 



354 FUEL 

if too fine, the crucible is too dense, and is apt to crack under 
the extreme changes of temperature to which it is exposed, 
and conducts heat slowly." The clay used is German. 
'' It is at once very fat, refractory, and wholly free from 
grit." 

The sand should be rather coarse, passing a screen of 
about 40 meshes to the inch. Burnt fire-clay has been found 
as good, but not better. 

The clay is made into a thin paste with water, the sifted 
sand and graphite are stirred in with a shovel, and the mass 
is mixed by means of a pug-mill. It is tempered by a few 
days' repose in a damp place, covered with cloths which are 
moistened occasionally. 

A weighed lump of the mass is slapped and kneaded, and 
put into the bottom of a thick plaster-of-Paris mould, the 
interior of which has the form of the exterior of the crucible, 
and centred on a potter's wheel. While it revolves, a cast- 
iron or steel profile of the interior of the crucible is lowered 
into the mass. The clayey mass is pressed against the sides 
of the mould, and raised gradually to its top, jointly by the 
revolution and by the moulder's hand. Any excess which 
comes above the top is cut off, and the lip is cut out. The 
crucible is left in the mould about three hours, the plaster 
absorbing its moisture, and thus stiffening it so that it can be 
handled. It is then air-dried for about a week in a warm 
room, and is fired. The firing takes a week ; one day is 
occupied in charging, three in firing, and two in cooling 
down. 

Firing Crucibles. — Crucibles, like all articles of pottery 
to be fired, are placed in earthen vessels or saggers, which are 
placed one above the other in the kiln. In the case of 
plumbago crucibles it is important to keep out air, so as to 
prevent oxidation of the graphite. For this purpose one 
sagger is often inverted over the other, some coke placed 
inside, and the joint luted with clay. The graphite should 
never be burned away more than just at the surface. 

Using Black -lead Crucibles. — Black-lead crucibles 



CRUCIBLES 355 

require careful annealing before use. The fire should be 
allowed to burn down, and some cold coke put on, the crucible 
put on this mouth downwards, covered with coke, and the 
fire allowed to burn up slowly till the crucible is well red-hot. 
The carbon will be burned away from the surface of the 
crucible, leaving it grey or white. 

Salamander Crucibles. — To avoid the necessity for 
annealing, the Morgan Crucible Company make crucibles 
known as the Salamander brand, which can be put into the 
fire at once without risk. They are covered with some 
waterproof glaze, probably a salt glaze, which answers its 
purposes thoroughly. 

Carbon Crucibles. — For experimental work, Deville 
used crucibles about 4 inches high, turned out of solid gas- 
retort carbon, which were placed in a clay crucible for use, 
but retained their form even if the outer crucible melted 
away. 

Brasqueing Crucibles. — Small crucibles for laboratory 
work can be readily lined with charcoal. 

Powdered charcoal is mixed with a mixture of equal parts 
of warm water and treacle till it is just stiff enough to cohere 
by pressure, and is firmly pressed into the crucible, and a 
cavity is cut out in the centre. A cover is put on and luted, 
and the crucible is heated to redness and allowed to cool. 
The lining will separate from the crucible, but will remain 
perfectly coherent. 

" Berthier states that he has occasionally fined crucibles 
with silica, alumina, magnesia, or chalk, previously moistened 
with water so as to make them sufficiently cohesive, and that 
a thin lining of chalk renders earthen crucibles less permeable 
to molten litharge." * 

Alumina Crucibles. — These crucibles may be made, accord- 
ing to Deville, by heating alumina and strongly ignited marble 
in equal proportions to the highest temperature of a wind- 
furnace, and then using equal proportions of the substance 
thus obtained, powdered ignited alumina, and gelatinous 

1 Percy, Fuel, p. HI, 



356 FUEL 

alumina. Such crucibles do not soften at the melting-point 
of platinum, and resist almost all corrosive materials. 

Lime Crucibles. — Lime crucibles are made by taking a 
piece of well-burned slightly hydrated lime, cutting it by 
means of a saw into a rectangular prism 3 or 4 inches on the 
side and 5 or 6 inches high. The edges are rounded off, and 
a hole is bored in the centre. 

Testing Clay as to its Fitness for Fire-brick and 
Crucible-making. — The clay must first be examined as to 
its plasticity by mixing a little with water and moulding it. 

The clay, if its plasticity be sufficient, is rolled out into a 
sheet, and triangular portions are cut out with a knife, care 
being taken to leave the edges quite sharp. These are dried, 
put into a black-lead crucible, and heated to the highest 
attainable temperature for some hours. They are then 
allowed to cool and examined, and if the edges show no 
sign of softening, the clay may be pronounced sufficiently 
refractory. 

For very refractory clays a higher temperature than that 
which can be obtained in an ordinary crucible furnace is 
required. A hot -blast gas furnace may then be used. 
Another method of testing clays is to grind finely, and mould 
into little prisms with varying proportions of some fluxing 
oxide, and the one which requires most oxide to make it 
fusible is the best clay. Richters tones up the clay with fine 
alumina till it is as refractory as a standard clay. 

The refractoriness is often measured by making the clay 
into little pyramids having a triangular base, the sides of 
which are § inch, f inch, and f inch, and the height 2| inches, 
and comparing their behaviour with Seger cones. 

If the clay is to be used for crucibles, the best method of 
testing is to make it into small crucibles in the apparatus 
described on p. 352, first burning some of the clay to mix 
with the raw clay drying and firing them, and then subjecting 
them to the various tests : — 

1. Heat to the highest possible temperature inclosed in 
another crucible. 



RETORT MATERIAL 357 

2. Heat to redness, take from the fire and plunge into 
cold water. 

3. Half-fill with litharge, heat to fusion, keep fused for 
about five minutes, then pour off the litharge, and examine 
how far the pot has been corroded. 

The finer the grain the better the pot will stand test 3, 
and the coarser the better will it stand tests 1 and 2. 

The Refractory Materials Committee of the Institution 
of Gas Engineers has carried out a considerable amount of 
research during the last twelve years on the subject of fire- 
bricks and retort material and has issued standard specifica- 
tions of great value both to manufacturers and users. The 
revised specifications are as follows : 

I. Retort Material 

1. The retorts, or retort-tiles, shall be made of a suffi- 
ciently seasoned raw clay and elean burnt-clay or " grog." 
No grog shall be used which will pass through a test sieve 
having 16 meshes to the linear inch. 

2. A complete chemical analysis of the material is to be 
provided by the manufacturer when required by the pur- 
chaser for his personal information only. 

3. A piece of the material shall show no sign of fusion 
when heated to a temperature not less than Seger cone 28 
(about 1630° C), the heat being increased at the rate of about 
50° C. per minute in an oxidizing atmosphere. 

4. All surfaces shall be reasonably true and free from 
flaws or winding ; and, after burning, no " washing " shall 
be done without the consent of the purchaser. The texture 
throughout shall be even and regular, containing no holes 
or flaws, and the " apparent porosity " shall not be less than 
1 8 per cent nor more than 30 per cent. 

5. The material shall be evenly burnt throughout and 
contain no black core. A test piece when heated to a 
temperature of Seger cone 14 (1410° C.) for two hours shall 
not show, when cold, more than 1J per cent contraction or 
expansion. 



358 FUEL 

The size of a representative test piece shall be 4J inches 
long by 4J inches wide, the ends being ground flat and the 
contraction measured by means of Vernier callipers reading 
to 01 mm., a suitable mark being made in the test piece so 
that the callipers may be placed in the same position before 
and after firing : 

II. Fire : bricks, Blocks, Teles, Etc. 

1. Two grades of material are covered by the speci- 
fication : 

(1) Material which shows no sign of fusion when 

heated to a temperature of not less than Seger 
cone 30 (about 1670° C). 

(2) Material which shows no sign of fusion when 

heated to a temperature of not less than Seger 
cone 26 (about 1580° C). 

2. Analysis as in I. 2. 

3. Freedom from flaws as in I. 4. 

4. A test piece when heated to a temperature of Seger 
cone 14 for two hours shall not show more than the following 
linear contraction or expansion : 

No. 1 grade 1 per cent, No. 2 grade 1 J per cent. The test 
piece shall be representative and measure 4J inches long by 
4| inches wide. 

5. In the case of ordinary bricks, 9 inches by 4J inches by 
3 inches or 2 J inches thick, there shall not be more than± 
1 \ per cent variation in length, nor more than ± 2 J per cent 
variation in width or thickness ; and in all cases the bricks 
shall work out their own bond, with not more than J-inch 
allowance for joint. 

In the case of special bricks, blocks, or tiles there shall 
not be more than ±2 per cent variation from any of the 
specified dimensions. 

6. The material shall be capable of withstanding a crush- 
ing strain of not less than 1800 lbs. per square inch. 

7. Cement clay shall be capable of withstanding the 



SILICA BKICKS, BLOCKS, TILES, ETC. 359 

same test for refractoriness. It may contain a suitable 
percentage of fine grog. 

8. All bricks, blocks, or tiles shall be distinctly marked by 
means of a figure 1 or 2 to indicate the grade to which they 
belong. 

III. Silica Bricks, Blocks, Tiles, Etc. 

The material covered by this specification is divided into 
two classes : 

(1) That containing 92 per cent and upwards of 

silica and called " silica " material. 

(2) That containing 80 to 92 per cent of silica, and 

called " siliceous." 

1. Test pieces of the material shall show no sign of fusion 
when heated to the following temperatures : 

" Silica " material — not less than Seger cone 32 (about 
1710° C). 

"Siliceous" material — not less than Seger cone 29 
(about 1650° C). 

Conditions as in I. and II. 

2. Analysis as in I. 

3. Freedom from flaws as in I. 

4. A test piece, at least 4| inches long by 4J inches wide, 
heated for two hours to a temperature of Seger cone 12 shall 
not show, on cooling, more than 0*75 per cent linear contrac- 
tion or expansion. 

5. Uniformity in measurement as in II. 5. 

6. Cement clay as in II. 7. 

The furnace recommended for testing purposes is one 
with Meker gas burners using compressed air at not less than 
10 lb. pressure per square inch, or Hirsch's electric furnace 
working at about 90 volts and 90 amperes. 

In testing for refractoriness it is advisable to make a 
preliminary test with a small conical piece of the material, 
using the small Seger cones 28, 30, and 32. 

As fire-clay materials have no well-defined melting- 
points, the temperature at which they begin to melt is 



360 



FUEL 



assumed to be that at which the edges of the materials lose 
their sharp angularity. 

Best china clay fuses between cones 35 and 36, and this 
may be used to cement the test piece and Seger cones on to a 
refractory slab in the test furnace. 

The " apparent porosity " is determined by means of 
the porosimeter made by Messrs. Gallenkamp & Co., 
London. The test piece should be about the size of half 
a brick. This is placed in a glass vessel fitted with a tap at 
the bottom and a close-fitting lid having a conical top. The 
tap is connected with a burette. 

The porosity is determined by placing the dried piece of 
brick in the vessel, evacuating the air by pump, and measur- 
ing the total volume of the brick and that of the pores only 
by immersion in paraffin oil. 

Refractoriness. — The practical man has long known that 
retorts and other fire-clay structures become deformed at 
temperatures very much lower than their melting-points as 
above defined. For example, it is dangerous to allow vertical 
retorts to attain, and maintain for any considerable length of 
time, a temperature of even 1300° C, although the material 
may be the best obtainable with melting or " squatting " point 
of 1700° or over. There may be little or no apparent fluxing, 
but serious damage may be done, especially to intermittent 
vertical retorts. Mellor and Moore published in vol. xv. (1915- 
16) of the Transactions of the English Ceramic Society very 
interesting experimental data on " The Effect of Loads on the 
Refractoriness of Fire-clays . ' ' The following are typical results : 



No. of 
Trial. 


Squatting 

Temperatures. 

No Load. 


Load in 
lb. per 
sq. in. 


Squatting 
Temperatures. 


Load in 
lb. per 
sq. in. 


Squatting 
Temperatures. 


Cone. 


°c. 


Cone. 


°c. 


Cone. 


°c. 


1 
2 
3 
4 
5 


29 
28 
31 
32 
30 


1650 
1630 
1690 
1710 
1670 


54 
54 

84 
84 
84 


15 
14 
16 
18 
16 


1435 
1410 
1460 
1500 
1460 


72 

72 

112 

112 

112 


13 
12 
13 
15 
13 


1380 
1350 
1380 
1435 
1380 



SILICA BRICKS, BLOCKS, TILES, ETC. 361 

In all the tests made with different clays it was found 
that the greater the load the lower the squatting tempera- 
ture. 

It was also found by the same investigators that the 
decrease in the squatting temperature with unit increase of 
load is directly proportional to the squatting temperature. 

The more siliceous the clay the less the difference between 
the squatting temperature with or without a load. 

M. Gary had previously found that at temperatures near 
1000° C. fire-bricks can withstand a greater compressive load 
than they can when cold. This accounts for the well- 
known fact that a red-hot crucible can withstand a blow 
which would shatter it if cold. It is evident that although, 
as the temperature rises, the crushing strength of fire-clays 
under load at first increases, it afterwards diminishes long 
before the melting-point is reached. 

Some objections had been raised to the testing of fire- 
bricks and retort material in an oxidizing instead of a reduc- 
ing atmosphere, as it is well known that ferrous iron has a 
far greater fluxing action than ferric iron. It is therefore 
to be anticipated that the contraction of a brick under 
reducing conditions will be greater than it is under oxidizing 
conditions. Recent researches (Mellor, Transactions of 
Institution of Gas Engineers, 1917) show that this is actually 
the case. Most silica bricks show an after-expansion when 
strongly heated ; this is somewhat less in a reducing atmos- 
phere than it is in an oxidizing one. 

In another investigation Mellor determined the sizes of 
fire-bricks in the cold and hot state (about 1100° C). Of 
25 silica and fire-bricks tested the greatest expansion was 
1-77 per cent and the least 0-26 per cent. Here the true 
thermal expansion, in some cases at any rate, may be obscured 
by effects due to the after-expansion or the after-contraction 
of the fire-brick taking place while the bricks are being 
measured. It is important to take into account the con- 
tinued alteration in the character of bricks when heated 
repeatedly or for a long time. 



362 FUEL 

The corrosive action of flue-dust on fire-bricks is a matter 
calling for the attention of all makers and users of fire-clay 
goods. The Refractory Materials Committee referred to 
have already published in the 1918 Transactions of the 
Institution of Gas Engineers the results of experiments 
carried out by Dr. Mellor. 

The tests were carried out at 1400° C. with a variety of 
dusts which are well known to cause corrosion. 

The general conclusions arrived at are as follows : 

The penetration caused by the dust is greater in fire-clay 
bricks than in silica bricks. The bond is usually attacked 
first and the coarser grains last. 

In silica bricks the depth of penetration by the dust 
is less where the grain is finer. In coarse - grained 
bricks it is only the bond that is attacked to any great 
extent. 

Iron oxide does not exercise any appreciable corrosive 
effect on silica bricks in an oxidizing atmosphere. In a 
reducing atmosphere ferrous silicate is formed and acts as a 
corrosive flux. Fire-clay bricks are more severely attacked 
by iron oxides than silica bricks. 

When the dust is such that it forms a surface glaze, the 
material is protected from further rapid attack. It is the 
practice of some retort makers, including the famous Stettin 
Company, to glaze the retorts in the interior. This is of 
distinct advantage for horizontal retorts which do not allow 
the glaze to flow to a lower level. Another benefit of the 
glazing is due to the fact that the retorts, otherwise very 
porous, are rendered impervious to the gas and thus effect a 
saving during the first few days of use. 

In the case of coke-ovens and vertical retorts fluxing 
agents, such as sodium chloride (common salt), which are 
usually present to a greater or less extent (0-01 to 0-25 per 
cent) in the coals, exert a powerful influence in shortening 
the life of the fire-clay material. Some coke-oven builders 
limit their guarantees of durability of the ovens to the use 
of coals which yield wash water (from the water used in 



SILICA BRICKS, BLOCKS, TILES, ETC. 



363 



compressing the coke) containing less than one gramme of 
sodium chloride per litre. 

The analyses of typical fire-clay and silica bricks are as 
follows : 









Fire-clay. 


Silica. 


Silica SiO a .... 64-5 


93-7 


Titanic oxide Ti0 2 . 






1-3 


0-3 


Alumina A1 2 3 






29-5 


2-0 


Ferric oxide Fe 2 3 






30 


0-8 


Magnesia MgO . 






0-4 


0-2 


Lime CaO 






0-3 


20 


Potash K 2 . 






0-6 


0-6 


Soda Na a O 






0-4 


0-4 



1000 



1000 



NOTES AND TABLES 



Heat Units 

British Thermal Unit . . 1 pound of water raised 1° F. 

Centigrade Unit (often wrongly 

called a calorie) . .1 „ ^, 1° C. 

Calorie . ... 1 gramme „ 1° C. 

Large calorie . . .1 kilogram „ 1° C. 

To convert Fahrenheit units into Centigrade units or to convert 
B.Th.U. per lb. into calories per kilogram : 

x I or 1-8. 

5 

To convert calories into B.Th.U. : 

x 3-968. 



Thermometer Scales 

Fahrenheit . F. P. of water =3 2° . B.P\ of water=212° 
Centigrade . F.P „ = 0° . B.P. „ =100° 

To find a reading F° on Fahrenheit scale corresponding to C° on Centi- 
grade scale, or vice versa : 

F=?C+32 or 1-8C+32, 
5 

C=^(F-32) or -5x(F-32). 

Mechanical Equivalent of Heat 

1 B.Th.U = 778 foot-pounds. 

1 Centigrade unit . . . =1400 ,, 

1 Large calorie . . =3087 „ 

1 Foot-pound .... =1-356 x 10 7 ergs. 

1 Horse-power = 33000 foot-pounds per minute = 7-46 x 10 9 ergs per second 

365 



366 



FUEL 



English and Metric Weights and Measures 



I Meti 


<e 








= 39-371 inches. 


»» 










= 3-2809 feet. 


»» 










= 1-0936 yards. 


»> 










= -00006214 mile. 


1 Litr< 


3 








= 61-027 cubic inches. 


„ 










= -035317 cubic foot. 


1 Gramme . 








= 15-432 grains. 


9* 










= -032151 Troy oz. 


>> 










. = -0022046 Avoir, lb 


To convert metres to inches 


. x 39-371 




inches to metres 






x 02540 


, 


kilograms to lb. 






x 2-2046 


, 


litres to gallons . 






x -2200 


» 


gallons to litres . 






. x 4-546 


, 


grammes to grains 






x 15-432 


> 


grains to grammes 






. x -06480 


> 


ounces to grammes 






x 28-349 



Specific Heat of Gaseous Substances at Ordinary Temperatures 

Air -2375 

Oxygen . -2175 

Nitrogen -2438 

Hydrogen 3-4090 

Carbon monoxide ...... -2450 

Carbon dioxide . . ■. . . . -2169 

Methane . . . . . . . . -5929 

Ethylene -4040 

Steam . . -4805 

Sulphuretted hydrogen ..... -2432 

Sulphur dioxide ...... -1540 



Weight of Oxygen and Air required for Combustion 





Oxygen. 


Air. 


One part by weight of — 






Carbon ..... 


2-67 


11-50 


Hydrogen ..... 


8-0 


34-5 


Carbon monoxide 


0-57 


2-46 


Methane . 


40 


17-2 


Ethylene 


3-43 


14-8 


Acetylene ..... 


308 


13-3 



1 The specific heat of a gas is the number of heat units required to 
raise the temperature of unit weight of it one degree (water = 1). 



NOTES AND TABLES 
Calorific Power of Various Combustibles 



367 





B.Th.U. 


C.U. 


One pound weight of — 






Carbon to carbon dioxide . . 


14600 


8110 


Carbon to carbon monoxide . 


4390 


2440 


Carbon monoxide to carbon dioxide 


4370 


2430 


Hydrogen to water 


61000 


33900 


Hydrogen to water vapour 


51500 


28600 


Methane to carbon dioxide and water 


23920 


13290 


Ethylene „ „ „ 


21310 


11840 


Acetylene „ „ „ 


20990 


11660 


Sulphur to sulphur dioxide 


4000 


2220 


Gross Value — 






Wood 


f 4500 to 
\ 7200 


2500 
4000 


Coal 


/ 10000 to 
\ 15000 


5560 


8330 


Anthracite ..... 


/ 12500 to 
\ 15000 


6940 
8330 


Coke 


/ 11000 to 
\ 14000 


6110 

7780 


Natural oil . 


18000 


10000 


Coal-gas ..... 


13500 


7500 



INDEX 



Absolute zero in thermometers, 275. 

Absorbing gas power of charcoal, 73. 

Acetylene, 6, n, 12. 

Acid refractory substances, 329. 

Advantages of gaseous fuel, 191. 

Air, amount required for combustion, 21, 262. 

— formula for velocity of chimney current, 262. 

— supporter of combustion, 5. 

— thermometers and Regnault's results, 278. 
Alcohol from coke-oven gas, 202. 

— importance of as fuel, 137, 138. 
Alkalies in fire-clay, 333. 
Alumina crucibles, 355. 

— in fire-clay, 334. 
American charcoal kilns, 81. 

— meilers, 81. 

Ammonia from non-caking coal, 59. 

— how obtained, 199. 

— recovery of , and Mond gas producer, 163. 
Analyses of American crucibles, 353. 
cellulose, 43. 

charcoal gas, 74. 

pile gas, 79. 

coal-gas tar, 198. 

Derbyshire fire-clay, 333. 

Etherley, 333. 

— — French Normandy, 333. 
Garnkirk, 333. 

Glenboig, 333. 

Poole, 333. 

producer gas, 173. 

Annual loss from use of by-product-destroying 

ovens, in. 
Anthracites, 54, 62. 

— analyses of, 59, 63. 
Anthracitic coals, 61. 
Appolt coke oven, 96. 

Archer process of making oil-gas, 189. 
Artificial gas, 140. 

forms of in present use, 140. 

Ash of coal, 66. 

composition of, 66, 67. 

peat, 47. 

wood, 44. 

Atomiser, Field- Kirby, 258. 

Australia's percentage of world coal, 55. 

Aydon's injectors, 257, 258. 

Baird and Tatlock's pyrometer, 293. 

Baku oil distilleries, 129. 

Baly and Chorley's thermometer, 277. 

Barnsley Low-temperature Carbonization Co., 

and smokeless fuel, 208. 
Barus, Dr. Carl, and bases for pyrometers, 272. 
Basic brick press, 345. 

— bricks, 345. 

— materials, 338-347. 
Batho furnace, 246. 
Battersea round crucibles, 349. 

( D 107 ) 



369 



Bauer coke oven, 99, 100. 
Bauxite, 339. 

— analysis for brick-making, 340. 

— bricks, 346. 
Becheroux furnace, 241. 

Becker and Serle's patent for smokeless fuel, 

205. 
Beckmann differential thermometer, 304. 
Beehive coke, density of, 84. 

ovens, 90. 

• annual numbers of, 112. 

application of, world-wide, 94. 

explanation of process, 93. 

gigantic loss of by-products, in. 

sources of loss, 96. 

the remedy of recovery ovens, in. 

Benzene, 12, 200. 

— Germany's consumption of, 200. 

— heat of combustion of, 32. 

— formation of, 32. 

Benzol and benzene, 136. 

— compared with petrol and alcohol, 138. 

— freezing point of, 137. 

— principal sources of, 136. 

Benzole, amount recovered from by-product 
ovens, 200. 

— products of, 200. 

Berthelot's calorimetric apparatus, 299. 
Berthelot-Mahler calorimeter, 303-305. 

improved in Mahler-Cooke bomb, 305. 

Berthier on brasqueing crucibles, 355. 

Berthier's calorimetry process, 297. 

Birch, analysis of, 43'. 

— relative fuel value of, 45. 

Bischof gas producer, 142. 

Bischof's refractory quotient of fire-clays, 335. 

—7 standard fire-clays, 335. 

Bituminous coals, 54-56. 

— — analyses of, 59. 
classified, 58. 

— wood, 55. 

Black-lead crucibles, 352. 
analysis of, 353. 

apparatus for making at Morgan's, 353. 

using, 354. 

Blast, Neilson's hot, 222. 
Blast or forced draught, 264. 
Blast furnace, 216. 

ammonia from, 209. 

amount of fuel to produce one ton of 

iron, 221. 

as gas producer, 179. 

calorific energy of, 220. 

chemical action in, 217. 

compared with gas-producer, 181. 

conditions of good working, 218. . 

determining temperature of hot-blast, 

280. 
economy of, 218. 

2 B 



370 



INDEX 



Blast furnace, efficiency of, Bell's figures, 
221. 

for iron-smelting, 216-221. 

for lead and copper smelting, 221. 

— — fuel for, 221. 

gas and ammonia-washers, 206. 

and oil-washers, 206. 

in gas-engines, 322. 

potash salts from, 202. 

treatment of, 203-207. 

— ■ yield of, 207. 

gases analysed, 179, 180, 191, 192. 

height of, 216, 218, 219. 

ratio to diameter, 216, 218. 

selection of fuel for, 219. 

spirit from, 209. 

tar extractor, 206. 

— — tar from, 195, 209. 

— — • — oil from, 130. 

type of gas-producers, 158. 

typical, 216, 217. 

water jackets, 221. 

Blind-coals, 61. 

Blue Billy, 340. 

Bodies with negative heat of formation, 36. 

Boetius furnace, 241. 

Boiler furnaces, 236-240. 

for liquid fuel, 257. 

— steam, 316. 

Boiling and melting points of various sub- 
stances, 293. 
Bone and M'Court's muffle furnace, 255, 256. 
Bovey lignite coal analyses of, 55, 56. 
Boys' gas calorimeter, 307-312. 
Brasqueing crucibles, 355. 
Brick mortars, 347. 

— press, basic, 345. 
Bricks, 340-347. 

— basic, 345. 

— dolomite, 345. 

— fire, 340. 

requisites of good, 340. 

— fire-clay, analysis of, 363. 

— ganister, 344. 

— silica, 344, 363. 

manufacture of, 344. 

Briquettes, 115-118. 

— analyses of, 115. 

— cost of making, 118. 

— manufacture of, 116. 
British thermal unit, 26. 
Brown coal, 54, 55. 
B.T.U., 26. 

Bull-dog, 340. 

Bunsen on rate of flame propagation, 16. 

Bunsen burner, 13. 

Professor Lewes on non-luminosity of, 

13-15- 

on its temperature, 13, 14. 

Burner, Aydon's. See Aydon's injectors. 

Butterfly value, 245. 

By-products aimed at, 193. 

destroying ovens, annual loss from, ur. 

— lost in Beehive ovens, 1 1 r . 

— recovery of, T93-202. 

— saved, ammonia, in, 178, 193-195, 199, 
200. 

from blast-furnaces, 59. 

gas-producers, 178, 193. 

benzol, in. 

benzole, 200, 201. 

crude benzole, 195. 

ethylene from coke-oven gas, 202. 

potash salts, 202. 

pure alcohol, 202. 

tar, 130, 195-199. 



By-products saved, tar, yield of from coal, 195, 
196. 

saving ovens, lists of, 90, 112. 

number in 1917 of British, 112. 

Caking coal, 56, 57. 

analysis of, 57, 58. 

cause of caking, 57. 

Calcining furnace, 224, 227. 
Calculation of calorific intensity, 37-41. 

calorific power, 29-37. 

evaporative power, 31. 

of hydrogen, 31. 

— — producer gas composition, 172, 173. 

analysed, 173. 

Callander's silica bulb thermometers, 279. 
Calorie, 26. 

Calorific intensity, defined, 37. 
formulae, 38-40. 

— power defined, 29. 
of hydrogen, 35, 37. 

and intensity related but not identical, 

39- 
of hydrogen and carbon compared, 

39, 40. 

at higher temperatures, 36. 

Cornu's formula, 40. 

etc., tables of, 72, 367. 

ethylene, 72. 

formulae and examples, 29, 30, 33-37. 

Gmelin's formula, 40. 

of carbon, 30. 

coal gas, 141. 

fuels containing oxygen and hydrogen, 

34, 35- 

gas from coke-fed blast furnaces, 180. 

gas, how to find, 139. 

hydrogen, 29, 37. 

— liquid fuels, 328. 

— solid fuels, 33, 34. 

— wood, 45. 

Calorimeters, Berthelot's apparatus, 299. 

— Berthelot-Mahler, 303. 
formula, 304, 305. 

— Berthier's process, 297. 

— Bomb, 305, 315. 

— Boys' gas, 307-312. 

— comparison of calculated and determined 
results, 314. 

— Darling, 303, 314. 

— for fuel gas, 305. 

— forms of recording gas, 313. 

— for very volatile liquids, 314. 

— Junker, 305-308. 
formula, 307. 

— Mahler-Cooke bomb, 305, 315. 

— Parr, 30 1. 

— recording gas, 313. 

— Rosenham, 303. 

— Rumford, 298. 

— Simmance-Abady gas, 313, 314. 

— Thompson's, 299, 315. 

— Wild, 301. 

— W. Thomson's oxygen, 301-303, 305. 
Calorimetric results, calculated and deter- 
mined compared, 314. 

Calorimetry, 297-315. 
Campbell gas generator, 166. 
Canada, percentage of world coal, 55. 
Candle flame, 10. 
Cannel coals, 51, 54, 62. 

examples of, 63. 

geology of, 51. 

— gas, analysed, 141. 
Carbocoal (Smith's patents), 209. 
Carbon, calorific power of, 30. 



INDEX 



371 



Carbon, combustion of, 30. 

— compared with hydrogen, 39. 

— in crucibles, when to be avoided, 348. 

— on ultimate analysis of, 328. 
Carbon-dioxide, effect on flames, 3. 

— in blast-furnace gases, 179. 

— in furnace gases and gaseous fuels, 328. 

— in same, found by W.R.C0 2 indicator, 328, 
329. 

Carbon-monoxide in coke-fed blast-furnace 

gases, 179. 
Carbonization at low temperature, 202-212. 

— of coal and yield of tar, 195. 
Carburetted water-gas, 189. 
Card of wood, value of (foot), 81. 
Casting sands, 347. 

analyses of, 347. 

Kaufman's, 347. 

Cast steel, crucible furnaces for, 233. 

Catalan forge, 223. 

Cause of caking in coal, 57. 

Cellulose, chief constituent of wood, 43. 

— analysed, 43. 

Centigrade or Celsius thermometer, 270. 

Centrifugal fan extractors, 197. 

Chain grate stokers, 237. 

Changes in passage from wood into coal, 64. 

Char, smithy, 94. 

Charcoal, 73. 

— absorbing gas power of, 73. 

— American kiln, 80. 

— as a fuel, 74. 

— burners, methods, and yields of compared, 
81. 

— burning, 76, 77. 
in Sweden, 78. 

— charring in kilns, 70 . 

— composition of, 74. 

— density of, 74. 

— distillation of in retorts, 82. 

— from peat, 82. 

— gas from, analysed, 74. 
charcoal kiln analysed, 79. 

— Pierce process, 80. 

yield of, 81. 

analysed, 81. 

— preparation of in circular piles, 75. 

explained, 75. 

rectangular piles, 77. 

theory of process, 78. 

— produced here as by-product, 82. 

— by distillation in retorts, 82. 

— red, 75.' 

— Thourer's theory of, 85. 

— yield of, 79. 

influence on, of burning rate and heat, 79. 

Chemical composition of coal, 69. 
Chemistry, thermal, 26. 

laws of, 27. 

Cherry coal, 60. 

Chimney draught, upward current explained, 

261. 

formula for, 263. 

effective area of, 263. 

velocity of, 262. 

China, percentage of world coal, 55. 
Chiswick (Del Monte) system and smokeless 

fuel, 210. 
Chloridizing roasting furnace (Stetefeldt), 233. 
Chlorine, 324. 

— in coal, 65. 
Chromite, 337. 

— analysed, 337. 

Classification of artificial gases, 140. 
bituminous coals, 58. 

blast-furnace type of gas-producers, 158. 



Classification of coals, 54. 
coke ovens, 90. 

— — fuels, 41, 42. 

furnaces for solid fuel, 212. 

gaseous fuels, 42. 

gas-producers, 143. 

liquid fuels, 42. 

natural fuels, 41. 

pyrometers, 272. 

Clay, carboniferous, 332. 

— composition of, 330. 

— for furnace building, 330. 

— origin of, 33 r. 

— testing for fire-brick and crucible-making, 
356. 

Cleaning the gas for gas-engines, 165. 
Closed-bottom gas-producers, 148. 

and the steam jet, 149. 

Coal analysis, how to find components, 322-326. 

ash, 323. 

chlorine, 324. 

moisture, 322. 

specific gravity, 325, 326. 

sulphur, 323. 

as calcium sulphate, 324. 

volatile matter and coke, 323. 

Coal and briquettes, 115. 

petroleum, heating values compared, 132. 

Coal, anthracite, 62. 
analysed, 63. 

— anthracitic, 61. 
analysed, 61. 

— ash, 66. 

analysed, 66, 67. 

— assay of, 322-326. 

— beds, 52. 

— bituminous, 54, 55, 56. 

analysed, 59. 

classified, 58. 

— brown or lignite, 54, 55. 
— ■ — • analysed, 56. 

— by-products recovered, nr. 

— caking, Percy's limits of, 58. 

— Canadian, Dawson on, 54. 

— cannel, 51, 62, 63. 

— carbonized, 1916, in by-product ovens, in. 

— chemical composition of, 69. 

— chlorine in, 65. 

— classification of, 54. 

— coking, 61. 

— compared with coke, 114. 

— compression, 109. 

— definitions of, 49. 

— distribution of, 54, 55. 

— furnace, 60. 

— — analysed, 61. 

— gas, 60. 

analysed, 61. 

in, 68. 

— geology of, 49. 

— Huxley on, 54. 

— lignite, 54, 55 ; analysed, 56. 

— long flame, 58, 59. 

— nitrogen in, 66. 

— non-caking, long flame, 58, 59. 
analysed, 60. 

coke from, 109. 

— passage from wood to, 64. 

— percentage of indifferent lands, 55. 

— phosphorus in, 66. 

— proximate analysis of, 322. 

— rarer elements in, 68. 

— relative C.P. with petroleum, 132. 

— selection of for blast furnaces, 219. 

— sorting small to sizes, 121. 

— structure of, 52, 53. 



372 



INDEX 



Coal,- sulphur in, 64 86. 

— valuation of, 70. 

— washing, 118-125. 

— water in, 64. 

— weathering of, 69. 

— yield of gas, 60. 
" Coal-brasses," 65. 
Coal-gas, 140. 

— amount yielded by coal, 60, 62, 140. 

— analyses of, 141. 

— calorific value of, 141. 

— cost, 140. 

compared with coal, 141, 142. 

— tar, average analysis of, 198. 

ultimate products of purified, 198, 

199. 
Coal-mine gases and their analyses, 64. 
Coal-pitch {i.e. pitch coal), 55. 
Coal-tar, coefficient of expansion of, 134. 

— yield of, 195, r96. 
Coal- washer, Robinson, 120. 
Coal-washing, 118-125. 

— jig machines, 121. 

— Liihrig jig, 121. 

— object of, 118. 

— principle of, 119. 

— results of, 124, 125. 

— trough machines, 120. 

— various other types, 124. 
Coalite, 87, 204 

— analysed, 88. 

— and smoke abatement, 204. 
Co-efficient of expansion, defined, 134. 
to be allowed for in fixing tonnage by 

volume, 134. 

for coal-tar, 134. 

petroleum, r34. 

water-gas tar, 134. 

Coke, 82. 

— American, for blast furnaces, 219, 220. 

— analyses of, 84, 326. 

— and coal, comparison of, 114. 

— as a fuel, 84. 

— burning in heaps, 88. 

— compared with charcoal, 82. 
coal, 114. 

— density of, 84. 

fed blast furnaces, gas from, analysed, 179. 

— from compressed coal, 109. 
non-caking coal, 109. 

— furnace {i.e. furnace coke), 83. 

— making in ovens, 90. 
stalls, 89. 

— nitrogen in, 86. 

— percentage of volume of pores to whole, 
326. 

— porosity of, 326. 

— properties of, 82. 
American, 220. 

— removal of sulphur from, 112. 

— selection of coal for making, 88. 

— soft, 83. 

— specific gravity of, 83, 326. 

— stall, Silesian, 89. 

— strength of, 84. 

— structure of, Thourer's theory, 85. 

— sulphur in, 86. 

— theory of oven process, 93. 
stall process, 89. 

— Thourer's theory of, 85. 

— to coal as charcoal to wood, 82. 

— varieties of, 83. 

— volatile matter in, 84. 

— volume of spaces in, 83. 
Coke-ovens, Appolt, 96. 

— Bauer, 99-101. 



Coke-ovens, Beehive, 95, 112 

modifications of, 94. 

sources of loss from, 95, 96. 

— by-products recovered from, in. 

— C.G.O., 90. 

— classification of, 90. 

— comparison of, in. 

— Connellsville, 95. 

— Coppde, 98. 

— Cox's, 90. 

— discharging, 93. 

— Huessener, 109. 

— Jameson, 90. 

— Koppers, 107. 

— losses from and remedy, 95, 96. 

— Otto, 90. 

— Otto Hilgenstock, 104. 

— Otto Hoffman, 103. 

— Pernolet, 90. 

— recovery of by-products from, 193-202. 

— Semet-Solvay, 107. 

— Simon-Carves, 101-103. 

— Simplex, 90. 

— theory of process, 93. 

— Welsh, 94. 

Coke quencher, Goodall machine, 112, 113. 
Coke-stall, Silesian, 89. 
Cokes, properties of some American, 220. 
Coking coals, 61. 

— in ovens, 90. 
stalls, 89. 

— stokers, 237. 

Colliery explosions and combustible dust in 

air, 2. 
Combustibles, calorific power of, 34, 35. 

— proportion of, 3. 
Combustion, 1-25. 

— amount of air for complete, 21. 

— complete and incomplete, 5. 
— - conditions of complete, 6. 
which favour, 1. 

— continuous, 4. 

— defined, 1. 

— effect of carbon-dioxide on, 3. 

— essential conditions of smokeless, 265. 

— formulae, 21-25. 

— heat carried off by gases, 24, 25. 

— incomplete, 6. 

— non-luminous, 13. 

— of carbon, 30. 

— commencing temperature of, 5. 

coal gas and air, 3. 

gases, 2. 

hydrocarbons, 6. 

hydrogen, 29. 

liquids, 2. 

liquid sprays, 2. 

— products of, 17, 24. 

removal of, 265. 

volume of, 25. 

— rate of in reverberators, 228, 229. 

— smokeless, 267. 

— supporters of, 1, 4. 

— temperature of, 4. 

— volume of products of, 25. 

— weight of air to burn 1 lb. of coal, 262. 
Comparison of calculated and determined 

calorimetric results, 314. 

carbon and hydrogen, 39. 

coal and coke, 114. 

coke ovens, in. 

Composition of. See also Analyses. 
Compounds, heat of formation of, 31. 

— negative heat of formation of, 36. 
Compression of coal, 109. 
Conditions for a good pyrometer, 271. 



INDEX 



373 



Conduction pyrometers, 285. 

Jourdes' method, 285. 

Cones, Seger, 281. 
Connellsville coke-ovens, 95. 
Contact heating, 20. 

— surface, influence of on burning, 3. 
Continuous combustion, 4. 
Conversion of heat into work, 316. 

— multipliers for English and Metric tables, 
Appendix. 

" Cooling-tube," in Siemens gas-producer, 145. 
Coppee coke, density of, 84. 

oven, 98, 99. 

Copper in ash of peat, 47. 
coal, 68. 

— melting furnace, details of, 227. 

— ore calcining furnace, 221, 224, 227. 

smelting in blast furnaces, 221. 

in water-jackets, 22 r. 

— refining coal furnace, details of, 227. 

wood furnace, details of, 227. 

Cord of wood, 81 (note). 

Cornish crucibles, 348 ; analysed, 349. 
Cornu-le-Chatelier pyrometer, 286. 
Cost of briquette-making, ri8. 

melting in oil furnaces, 260. 

oil fuel, 131. 

working suction gas-producers, 169. 

Couples for heat recording, 294. 

Cox's coke oven, 90. 

Crampton's method of burning powdered fuel, 

260. 
Creosote oils, effect on tars, 134. 
Crucible furnaces, 233, 234. 

Morgan's annular hot-air, 234. 

tilting, 234. 

Crucibles, 348-357- 

— alumina, 355. 

— Battersea round, 349. 

— black-lead, 352, 353. 
using, 354. 

— brasqueing, 355. 
Berthier on, 355. 

— carbon, 355. 

— clay, 348. 

— Cornish, 348. 
analysed, 349. 

— firing, 354. 

— Hessian, 350. 

— lime, 356. 

— London, 349. 

— manufacture of, 350. 
for steel-melting, 351. 

— materials for making, 350. 

— plumbago, 352. 

— qualities required in good, 348. 

— Salamander, 355. 

— selection of materials for, 350. 

— skittle pot, 349. 

— small, for laboratory use, 352. 

— steel -melting, 35 r. 

— testing clay for, 356. 
Crude mineral oil, 129. 

Cubillo's general balance of reverberatory 

furnaces, 230, 231. 
Cupellation furnace, details of, 227. 
Cutting and preparing peat, 48. 
Cyclone tar extractors, 197. 

Dairy, Bauer coke oven at, 100. 

Daniell's pyrometer, 273. 

Darling calorimeter, 314. 

Davy's theory of flame luminosity, 8. 

Dawson gas producer, 159. 

Degree of temperature denned, 270. 

Dehydration of tar, 198. 



Dellwik-Fleischer water-gas producer, 184. 

Dellwik's description of, 185. 

Density of charcoal, 74. 

coke (Beehive), 84. 

(Coppee), 84. 

peat, 47. 

Derbyshire fire-clay, analysed, 333. 
Determination of carbon dioxide in furnace 

gases and gaseous fuels, 328. 
Deville and Troost's iodine pyrometer, 278. 
Deville on alumina crucibles, 355. 
Deville 's experiments on flames, 16, 18. 

recorded results, 18. 

slowness of ignition explained, 17. 

Diesel oils, 135. 

Dinas bricks, Percy on manufacture of, 344. 

— rock, 329. 

Disadvantages of gaseous fuel, 193. 
Dissociation, 17. 

— Deville 's experiments, 18. 

— losses in gas producers, 174. 
Distillation of charcoal in retorts, 82. 
wood, 44. 

— to recover ammonia, double steam required, 
193- 

Distilled petroleums, 129. 

yield of, 129. 

Distilling zinc, retort furnace for, 236. 

Distribution of coal, 54. 

Dolomite, or magnesian limestone, 338. 

— analyses of, 338. 

— bricks, 345. 

Domestic fire, causes of smoke, 19. 
Dowson gas producer, 152, 153. 

— suction gas producer, 165, 166. 
Draught, blast or forced, 264. 

— velocity of up-chimney, 263. 
Duff gas producer, 160. 

Dumas method for determination of nitrogen, 
328. 

Dundonald's (Lord) patent attempt at smoke- 
less fuel, 205. 

Dunnacbie's regenerative gas kiln, 342. 

Duplex gas producer, Thwaite's, 157. 

Ebelmann's gas producer, 158. 

" Economical " carburetted water-gas plant, 
189. 

Efficiency of regenerative furnaces, 251. 

Krause's figures, 251. 

Thwaite's calculations, 255. 

diagrams, 254. 

Electric pyrometers, 290. 

Elements, rarer, in coal, 68. 

Elevated cooling tube in Siemens gas pro- 
ducer, 145. 

Endothermic reactions, 26. 

Energy lost in Beehive coke oven, 96. 

Engines, gas, 320. 

— oil, 322. 

— steam, 318. 

Etherley fire-clay, analysed, 333. 
Ethylene, 6. 

— flame of, n. 

— from coke-oven gas, 202. 

— luminosity of coal gas mainly due to, n. 

— velocity of explosion for complete combus- 
tion, 17. 

Eutectoid steel, heating and cooling curve of, 

294. 
Evaporative power, 31. 

of carbon, 31. 

hydrogen, 31. 

Excess of steam in gas producers, 175. 

Exothermic reactions, 26. 

Expansion for pyrometry of gases, 277. 



374 



INDEX 



Expansion for pyrometry of liquids, 274. 

mercury, 275. 

solids, 273. 

Expansion of iron, formula for, 273. 

Explosion, 17. 

Explosions of first order, 16. 

mixture of hydrogen and oxygen, 18. 

second order, 17. 

— velocities of, found by Dixon, 17. 

— violence of, and rate of ignition, 17. 

Fahrenheit thermometer scale, 270. 

Foil of equal-sized bodies in water, rate of, 119. 

Fans, 265. 

" Fat " coals, 60. 

Felspar, 331. 

— composition of, 331. 
Ferric oxide in fire-clay, 334. 
Fery absorption pyrometer, 287. 

— radiation pyrometer, 295. 

— spiral pyrometer, 296. 
Field- Kirby atomiser, 25S. 
Fire, domestic, 19. 

Fire-brick expansion under heat, Mellor on, 361. 

— making, testing clay for, 356. 
Fire-bricks, 340. 

— corrosive action of flue-dust on, 362. 

— hot and cold, Mellor on size of, 36 r. 

— requisites of good, 340. 
Fire-clay bricks, 341. 
analysed, 363. 

manufacture of, described, 341. 

Fire-clays, 332. 

— alkalies in, 333. 

— alumina in, 334. 

— analysis of Stourbridge, 332. 
various others, 333. 

— Bischof's refractory quotient, 335. 

— impurities in, 333. 
combined effect of, 335. 

— lime and magnesia in, 333. 

— oxide of iron in, 334. 

— titanic oxide in, 334. 
Fire-stones, 330. 
Firing crucibles, 354. 
Flame, 6. 

— acetylene, 12. 

— Bunsen, 13. 

— Bunsen's experiments on speed of, 16. 

— candle, 10. 

— compound, 7. 

— Davy on luminosity of, 8. 

— Deville's experiments on, 16-18. 

— ethylene, n. 

— Frankland on luminosity of, 9. 

— Lewes and Smithells' researches on, 9. 

— luminosity of, 8, 9. 

— methane, n. 

— Percy's definition of, 7. 

— propagation, 15. 

— simple and compound, 17. 

— structure of luminous gas, 10. 

— what takes place in a gas, 12. 
Flash point of liquid fuels, 327. 
Fletcher's patent furnace, 234. 

Flue dust, corrosive action of on fire-bricks, 362. 
Forced draught, 264. 
Formulas for calculating : 

— air required for combustion, 21-24. 

— calorific intensity, 37-39. 

— calorific power at high temperatures, 36, 37. 
by Berthelot-Mahler calorimeter, 303- 

305- 

Junker's calorimeter, 307. 

Rumbord's calorimeter, 298. 

Cornu's formula, 40. 



Formulae for calculating : 

■ — calorific power, Gmelin's formula, 40. 

■ of gaseous fuels, 35, 36. 

solid fuels, 33-35, 40, 4r. 

— chimney-draught, 262, 263. 

— expansion linear of solids, 273. 

— heat carried away by gases, 24, 25. 

— porosity, 326, 327. 

— rate of fall in water of bodies equal in volume,, 
unequal in weight, 119. 

— specific gravity, 325, 326. 

— temperature by Krupp's pyrometer, 284. 

method of mixtures, 282. 

Siemens' pyrometer, 282. 

— weight of products of combustion, 24. 
France, Belgium, etc.'s percentage of world 

coal, 55. 
Frankland's theory of luminosity of flame, 9. 
Fraunhofer C line in pyrometry, 289. 
Fremy's researches on composition of coal, 70.. 
French Normandy fire-clay analysed, 333. 
Fuel, advantages of gaseous, 191, 193. 

— calorific power of solid, 33. 

— Carl Wegener's powdered, 261. 

— classification of, "41. 

— coal, 48-71. 

— coke as, 82. 

— Crampton's powdered, 260. 

— disadvantages of gaseous, 193. 

— furnaces for liquid, 257. 
powdered, 260. 

— gaseous, 138-193. 
classification of, 42. 

— gases used for, 186-193. 

— heating power of, 26-4T. 

— liquid, 42, 126-138. 

— nature of, 41. 

— oils as, 131, 132. 

coefficient of expansion of, 134. 

for internal combustion engines, 135.. 

— peat as, 48. 

— pyrites as, 71. 

— relative value of woods as, 45. 

— solid prepared, 73-118. 

— spent tan, straw, etc. as, 46. 

— testing of, 322-329. 

— used per h.p. in steam-engines, 319. 

— utilization of, 315-322. 

— valuation of, 70. 

— wood, 42. 

— wood used as, 45. 

natural fuel of man, 42. 

Fuel gas, calorimeters for, 305. 
Furnace coals, 60. 

— coke, 83. 

analyses of, 84. 

specific gravity of, 83. 

— gases, C0 2 in, 328. 

— linings, 329, 335, 346. 

bauxite, 339. 

bull-dog, 340, 347. 

calcined flints, 336. 

Dinas rock, 329. 

dolomite, 346. 

fire-clays, 329. 

flint, 329. 

ganister, 335, 346. 

iron-ore slag, 347. 

lime, 338. 

magnesian limestone, 338. 

magnesite, 339. 

sandstones, 329. 

white sand, 336. 

Furnaces, action of regenerative, 2501.. 

— automatic stoking, 237. 

— Batho, 246. 



INDEX 



375 



Furnaces, Becheroux, 241. 

— blast, 216-222. 

— Boetius, 241. 

— boiler, 236. 

— Bone and M'Court's muffle, 255, 256. 

— calciner (copper ores), 227. 

— classification of difficult, 212. 

— CO2 in furnace gases and gaseous fuels, 328. 

— coking stokers for, 237-240. 

— copper refining (coal), 227. 
(wood), 227. 

smelting, 224. 

— crucible, 233. 

— Cubillo's reheating, 227. 

— cupellation, details of, 227. 

— details of typical, 227. 

— distributing heat in, 252. 

— efficiency of regenerative, M. Krauseon, 251. 

— Fletcher's patent, 234. 

— Flintshire lead, 227. 

— for gaseous fuel, 240-257. 
liquid fuel, 257-260. 

metallurgical purposes, 212-261. 

powdered fuel, 260, 261. 

solid fuel, 212-240. 

— fuel consumption in, 221, 228, 229. 

— Gjer's calcining kiln, 213, 214. 

— Gorman's heat-restoring gas, 249. 

— heat carried off by regenerators, 253. 

— hot blast for, 222. 

— injectors for oil-fired, 257, 258. 

— iron-smelting blast, 216. 

— kiln, 213-216. 

— lead and copper smelting blast, 221, 222. 

— losses of heat in, 252, 253. 

— Meldrum " Koker " stoker, 237, 238. 

— melting (copper), 227. 

— metallurgical, 212-261. 

— muffle, 234. 

— oil-fired steel (Steele-Harvey), 259. 

— Otto-Hoffman calcining kiln, 215. 

— Piat oscillating, 235. 

— Ponsard, 249. 

— position of regenerators in, 250. 

— Proctor's sprinkling stoker, 239. 

— puddling, details of, 227. 

— rates of combustion in, 229. 

— refining, 223. 

— reheating, Major Cubillo's, 227. 

— retort, 235. 

— reverberatory, 224. 

details of typical, 227. 

general balance of, 230. 

rate of combustion in various, 229. 

— Rockwell oil, 258. 

Quigley's results from, 259. 

— Scotch iron-ore kiln, 213, 214. 

— Siemens' new form, 246-248. 

" Hackney " port, 247. 

regenerative, 242. 

at Wishaw, 243. 

Head and Pouf 's variation, 247. 

— Siemens, Friedrich, 246. 

— Steele-Harvey oil, 259. 
Krause's test figures, 260. 

— Stetefeldt, 232, 233. 

— surface combustion, 255. 

— table of typical, 227. 

— thermal efficiency of, 251. 

— Thwaite's Ideal, 248. 
diagrams for, 254. 

— — efficiency calculations of regenerative, 
255- 

— using town gas, 256. 

Fusion for temperature of hot-blast, 280. 

— in reverberatory furnaces, 226. 



Fusion metals and alloys suitable for, 280. 

— pyrometers, 280. 
Future of oil fuel, 131. 

Gallenkamp's porosimeter, 360. 
Ganister, 335. 

— analysis of, 335, 336. 

— bricks, 336, 344. 

— for furnace linings, 335. 
Garnkirk fire-clay analysed, 333. 

Gary on fire-brick strength at high tempera- 
tures, 361. 
Gas, artificial, 140. 

— blast-furnace, 179-181. 
in gas engines, 322. 

— calculating composition of, 172. 

— calorimeters for fuel gas, 305. 

— cleaning the, 168. 

— coals, 58-60. 
analysed, 59, 61. 

— coke, 83. 

— firing of boilers, 257. 

— flame, Lewes and Smithells' researches, 9. 
what takes place in a, 12. 

— for gas-engines, 165. 

— from charcoal analysed, 74. 
pile analysed, 79. 

— ■ — coke-fed blast furnaces analysed, 179-1S1. 
C. P. of, 180. 

— — Northumberland and Durham coals 
analysed, 68. 

■ — in coal, 68. 

— lighting back, avoidance of, 169. 

— Mond, 176. 

— natural, 138, 191. 

— oil, (i.e. oil-gas), 189. 

— producer {i.e. producer-gas), 142. 

— water, (i.e. water-gas), 181. 
Gas-engines, 320-322. 

— Atkinson, 321. 

— blast-furnace gas in, 322. 

— cleaning the gas for, 168. 

— converting potential into actual energy in, 
320. 

— cost of working, 169. 

— Crossley, 321. 

— gas for, must be cleaned, 165, 168. 

— more economical than steam-engines, 321. 

— Otto, 320, 321. 
cycle of, 320, 321. 

— Tangye, 321. 

Gaseous fuels, 138-193, 328. 

advantages of, 191. 

classification of, 42. 

disadvantages of, 193. 

■ furnaces for, 240. 

Gases, composition of combustible, 190-192. 

— expansion of, 277. 

— found in coal-mines, 64. 

— from Northumberland and Durham coals, 
68. 

analysed, 68. 

— heat carried away by, 24. 

— used as fuels, analyses of, 190-192. 
Gas-fire, Mond's, 240. 

— flame, 7. 

Gas-kiln, Dunnachie's regenerative, 342. 
Gas producers, 142-186. 

and blast-furnaces compared, 181. 

Bischof, 142. 

blast-furnace type of, 158. 

blast-furnaces as, 179. 

by-products from, 193, 201. 

calculation of composition of gas from, 

172. 
Campbell suction, 165, 166. 



376 



INDEX 



Gas producers, classification of, 143. 

cleaning the gas from, 168. 

compared with blast-furnaces, 181. 

cost of working, 169. 

Dawson, 159. 

Dellwik-Fleisher, 184. 

Dowson, 152. 

suction, 165. 

Duff, 160. 

Ebelmann's, 158. 

enriching the gas by steam, 170. 

Ingham, 155. 

Loomis, 183. 

loss of heat in, sources of, 1 73-1 75. 

Kerpeley, 164. 

Kramer and Aarts' water-gas: generators, 

186. 

Mond, 162. 

Perry, water-gas generators, 188. 

Siemens', 143. 

circular, 148. 

closed bottom, 148. 

improvements on, 147. 

seeming loss of heat explained, 170. 

steam jet in, 149. 

Smith and Wincott, 162. 

solid bottom, 153. 

sources of loss of heat in, 173. 

starting, 168. 

Strong, 184. 

■ suction, 165-168. 

Taylor revolving bottom, 156. 

Thwaite duplex, 157. 

simplex, 152. 

small power, 160. 

steam jet for, 151. 

use of steam in, 170. 

water-bottom, 159. 

water-gas, at Leeds Forge, 182. 

Watt, 167. 

Wilson, 153. 

automatic, 155. 

working the, 175. 

yield of by-products from, 193, 197-201. 

Geology of coal, 49. 

Germany's percentage of world coal, 55. 

Gjers' kiln, 213, 214. 

Glenboig fire-clay analysed, 333. 

— regenerative gas-kiln, Dunnachie's, 342, 343- 
Goodall coke-quenching and loading machine, 

ri2, ri3. 
Gorman's heat-restoring gas furnace, 249. 
Graphite, 336. 

— analyses of, 337. 

Great Britain's percentage of world coal, 55. 
Greatest energy, law of, 29. 
Griiner's classification of coals, 58. 

" Hackney " port in Siemens' furnace, 247. 

Haematite, 340. 

Head and Pouf 's variation of Siemens' furnace, 

247. 
Heap-burning for coke, 88. 
Hearths, 212, 222, 223. 

— refinery, 223. 

Heat, balance sheet of for reverberatory 
furnaces, 230. 

— bodies formed with absorption of, 36. 

— British unit of, 26. 

— carried off by gases, 24, 174. 

— conversion of, into work, 316. 

— distribution of in an ironworks, 252. 

— efficiency of iron-smelting blast-furnace, 
80 per cent, 22r. 

— equivalent in work, 315. 

— evolution or absorption of, 27. 



Heat in reverberatory furnaces, 224. 

— lost by radiation, 174. 
in ash, 70, 71. 

in Beehive ovens, 95, 96. 

in gas producers, sources of, 173-175. 

heating furnaces, 252, 253. 

on conveyance into steam, causes of, 317. 

— measurement of, or pyrometry, 268-297. 

— mechanical equivalent of, 315. 

— of formation of benzene, 32. 
compounds, 31. 

Heating and cooling curve recorders, 294. 

— by contact or radiation, 20. 

— power of fuels, 26-41. 
natural gas, 138. 

— values of petroleum and coal compared, 132. 
Hessian crucibles, 350. 

Holmes washers, 199. 
Hot blast, 222. 

detennining temperature of, 280-284. 

by fusion pyrometer, 280, 281. 

— Krupp's pyrometer, 283, 284. 

Huessener coke-oven, 109. 

Humphries and Glasgow water-gas producer, 

189. 
Hydrocarbons, combustion of, 6. 

— in coke-fed blast-furnace gases, 179. 
Hydrogen and oxygen, explosion of, 18. 

— combustion of, 29. 

— compared with carbon, 39. 

— evaporative power of, 31. 

— on ultimate analysis of, 328. 

— water the only compound of, 5. 

Ideal furnace (Thwaite's), 248, 249. 
Ignition of coal, spontaneous, 69. 
Impurities in fire-clay, 333. 

combined effect of, 335. 

Ingham gas producer, 155. 
Injectors for liquid fuel (Aydon's), 258. 
Internal combustion engines, oil fuel for, 135. 
Iodine and porcelain globe pyrometers, Deville 

and Troost's, 278. 
Iron, formula for expansion of, 273. 

— in ash of peat, 47. 
Iron-ore kiln, Gjers', 213, 214. 
Scotch, 213, 214. 

— slag, for furnace linings, 347. 
Iron ores for furnace linings, 340. 
Iron oxide in fire-clay, 334. 

ganister, 335. 

Iron-smelting blast-furnaces, 216, 221. 
efficiency of, 221. 

Jet, Thwaite's annular steam, 151, 152. 
Jig coal-washing machines, 121-124. 

Luhrig process, 121-124. 

Jourdes' conduction pyrometer, 285. 
Juleff's Cornish crucibles, 348. 
Junker's calorimeter, 305-308 

formula, 307. 

new type, 307, 308. 

Kaolin, 331, 332. 
Kaufman's casting sand, 347. 
Kerosene, 129. 
Kerpely gas producer, 164. 
Kilns, 213. 

— American charcoal, 79, 81. 

— charring in, 79. 

— Gjers', 213, 214. 

— Otto Hoffman, 215. 

— Scotch iron-ore, 213, 214. 

Kjeldahl method for determination of nitrogen, 

328. 
" Koker " stoker, Meldruin's, 237. 



INDEX 



377 



Kopper's coke oven, 107. 

Kramer and Aarts' water-gas producer, 186, 187. 

Krause, J. W.'s figures of Maryland steel 

furnace, 260. 
Krause's figures of furnace efficiency, 251. 
Krupp's formula for temperature, 284. 

— pyrometer, 283. 

Laws of thermo-chemistry, 26. 

thermo-dynamics, 316. 

Lead-smelting blast-furnace, 221, 222. 

Le-Chatelier pyrometer, 286. 

Leeds Forge water-gas plant, 182. 

Lewes and Smithells on flames, 10-15. 

Light intensities in Wanner pyrometer, 288- 

290. 
Lignite, analyses of, 56. 

— or brown coal, 54, 56. 
Lime in fire-clay, 333. 

Liquid fuel, furnaces for, 257-260. 
Liquid fuels, 126-138. 

for small furnaces, 258. 

injectors for, 257, 258. 

to find calorific power of, 328. 

flash-point of, 327. 

specific gravity of, 327. 

Liquids, expansion of and pyrometry, 274. 
Livesey washer, 199. 
London round crucibles, 349. 

— triangle crucible, 349. 
Long-flame coal, 58, 59, 60. 
Loomis' water-gas producer, 183. 

and 200 cubic feet of gas for a penny, 

184. 
Loss of heat in Beehive coke-ovens, 103. 

gas producers, 173. 

Low-temperature carbonization, 202-212. 
and smokeless fuel. See Smokeless fuel, 

attempts at. 
Luminosity of flames, 8. 

• — acetylene, 12. 

Bunsen, 8, 13. 

coal-gas, 11. 

compound, 7. 

simple, 7. 

theory of Davy, 8. 

Frankland, 9. 

Lewes, 13, 14. 

Smithells, 10. 

Magnesia in fire-clay, 333. 
Magnesian lime, 346. 
Magnesian limestone, 338. 

analysed, 338. 

improperly called dolomite, 338. 

Magnesite, 330, 339. 

— analyses of, 339. 

Magnesium, very brilliant light of, 6. 
Magnetite, 340. 
Mahler-Cooke bomb, 305. 
Manufacture of briquettes, 116. 

cost of, 118. 

crucibles for steel-melting, 351. 

Marsh gas (foot), 3, 4. 

and air, proportion for explosion, 3, 4. 

in coal, 68. 

coal-mine gas, 64. 

Mechanical dash washers, 200. 

— equivalent of heat, 315, 365. 

— stokers, 236, 237, 266. 
Meldrum's " Koker," 237. 

Meilers, yield of charcoal from American, 81. 

Swedish, 81. 

Meldrum furnace, 237, 238. 
Meldrum's " Koker " stoker, 237, 238. 
Mellor and Moore on fire-clays, 360. 



Mellor on sizes of fire-bricks hot and cold, 361. 
Melting furnace (copper), 227. 
Mercury, expansion of, 276. 

— thermometer, 275. 

absolute zero, 275. 

Mesure and Noel's pyrometer, 288. 

Metals and alloys for hot-blast pyrometers, 

280. 
Methane, flame of, n. 

— velocity of explosion for complete combus- 
tion of, 17. 

Method of recovering by-products, 193. 
Mexican petroleums, 132. 
Millstone-grit, 330. 
Mineral oils, 126. 

Mixtures, method of in pyrometry, 282. 
Modifications of Beehive coke-oven, 94. 
Moisture in coal assay, 322. 
Mond gas, analyses of, 176. 

producer, 162, 163. 

and ammonia recovery, 163. 

Mond's gas fire, 240. 

Morgan's annular hot-air furnace, 234. 

— tilting furnace, 234. 
Mortars, 347. 

— rules for choice of, 347. 
" Mother of coal," 54. 
Motor spirit, 135. 

vast quantities obtained, 132. 

Moulds, Kaufman's sand for, 347. 
Muffle furnaces, 234, 235. 
Piat's oscillating, 235. 

Naphtha, yield of from distilled petroleums, 

129. 
Natural gas, 138. 
— - — analyses of, 139, 191. 

calorific power of, 139. 

large quantity escaping, 138. 

— oils, 126. 

Nature of by-products aimed at recovering, 
193- 

fuels, 41. 

Negative heat of formation, bodies with, 36. » 
Neilson's hot blast, 222. 
Neutral refractory materials, 336. 

— substances, 330. 
New-form Siemens' furnace, 247. 
Nitrogen determined by Dumas' method, 328. 
Kjeldahl's method, 328. 

— in coal, 66. 
coke, 86. 

coke-fed blast-furnace gases, 179. 

— ultimate analysis of, 328. 
Non-caking coal, analyses of, 56, 57. 
coke from, 109. 

examples of, 60. 

long flame, 58, 59, 60. 

Non-luminous combustion, 13. 
Normandy fire-clay analysed, No. 3, 333. 
Northumberland and Durham mines, gas from, 

68. 
Nut-washing jigs, 122. 

Oak, analysis of, 43. 
Object of coal-washing, 118. 
Occurrence of petroleum, 127. 
Oil, analyses of, 132. 

— distilleries, Baku, 129. 

— from blast-furnace tar by distillation, 129, 
130. 

— furnace for steam boiler, 257-260. 

— heavy and light, 133. 
Oil-engines, 322. 

— Diesel, 322. 

— Priestman, 322. 



378 



INDEX 



Oil fuels, advantages of, 131. 

calorific power of, 132. 

creosote, 134. 

crude mineral, 129. 

disadvantages of, 131 

essential qualities in, 132. 

evaporative power of, 132. 

for internal combustion engines, 135, 322. 

future of, 131. 

natural, 126. 

petroleum, 126. 

Pintsch process of making, 190. 

prepared, 129. 

shale, 130. 

solar, 129. 

Oil-gas, analysed, 141, 190. 

— Archer process, 189. 

— Pintsch process, 190. 

Oil (petroleum), preparation of by distillation, 

129. 
products, total imports IQ13 and 1918 of, 

127. 

world's output in 1917 of, 126, 127. ■ 

Optical pyrometers, 285. 
Ore kiln, Scotch iron-, 214. 
Origin of clay, 331. 

petroleum, 128. 

Oscillating furnace, Piat's, 235. 
Otto gas-engine, 320. 

four stages of its cycle, 321. 

Otto Hilgenstock coke oven, 104. 
Otto Hoffman coke oven, 103, 104. 

kiln, 215. 

Ovens. See Coke-ovens. 

Oxygen and hydrogen, temperature for 

explosion, 4. 
Oxygen calorimeter, Thompson's, 299. 

— essential to combustion, 1. 

— ultimate analysis of, 328. 

Parker's coalite patent for smokeless coal, 205. 
Parr calorimeter, 301. 
Passage from wood to coal, 63. 

Dr. Percy's stages of, 64. 

Peacock anthracite coal, 62. 
Peat, analysed, 47. 

— as fuel, 48. 

— ash of, 47. 
minerals in, 47. 

— charcoal, 82. 

— composition of, 46, 47. 

— cutting and preparing, 48. 

— density of, 47. 

— how formed, 46. 

— minerals in, 47. 

— moisture in, 46. 

— weight of in various states, 48. 
Pelouze & Audouin tar extractor, 197. 
Pennsylvania petroleum, analysed, 126. 
Percy on analyses of gas in coal, 68. 
Percy's analyses of lignite coals, 56. 
Perry watervgas producer, 188. 
Petrol, 135. 

— compared with alcohol and benzol, 138. 

— low boiling point of, 136. 

Petroleum and coal heating values compared, 
132. 

— calorific power of, 132. 

— Caucasian light, 132. 

— composition of, 126, 132. 

— distilled, 135. 

— imports 1913 and 1918, 127. 

— occurrence of, 127. 

— origin of, 128. 

— Pennsylvania crude, 126, 132. 

— products, imports of, 127. 



Petroleum, Russian, 126. 

— world s output of, 126. 
Phosphorus in coal, 66. 

— low ignition temperature of, 4. 
Photographic recorders, 294. 

Piat's oscillating muffle furnace, 234, 235- 

Pierce charcoal process, 80. 

Piles, charring in, 75. 

Pintsch process of making oil-gas, 189. 

Pitch coal, 55. 

Plumbago crucibles, 352. 

— manufacture of, at Messrs. Morgan's, 353. 
Ponsard furnace, 249. 

Poole fire-clay, 333. 
Porosimeter, Gallenkamp's, 360. 
Porosity, determination of, 360. 

— of coke, 326. 

Position of regenerators, 244. 
Potash salts from blast-furnace gas, 202. 
Powdered fuel, Crampton's method of burning, 
260. 

Wegener's patent, 261. 

Power, calorific, 29. 

— evaporative, 31. 

Premier tarless fuel process, 205. 

Preparation of charcoal in American kilns, 81. 

American meilers, 81. 

circular piles, 75. 

kilns, 79. 

retorts, 81. 

Swedish meilers, 81. 

Prepared fuel oils, 129. 
Preparing peat, 48. 
Prevention of smoke, 265-268. 
Priestman oil-engine, 322. 
Principle of coal-washing, 119. 
Proctor's sprinkling stoker, 239, 240. 
Producer-gas, 142. 

— analysed, r73. 

— analysis of Siemens', 144. 

— compared with blast-furnace gas, 181. 
water-gas, 186. 

— enriched by steam, 142. 

— first attempt to make by Bischof, 142^ 

— low calorific power of, 142. 

— washed for ammonia, 199. 
Producers. See Gas producers. 

— solid-bottom type, 153. 
Products of coal distillation, 140. 

combustion, 24. 

removal of, 265. 

Propagation of flame, 15. 
Properties of coke, 82. 

matter used in pyrometry, 272. 

Proportion of combustible, 3. 
Proximate analysis of coal, 322. 
Puddling furnace, 227. 
Pure alcohol from coke-ovens, 202. 
Pyrites as fuel, 71. 

— breaking effect of, on coal, 69. 

— presence in coal of iron-, 65. 

— removed from coal, 124. 
Pyroligneous acid and charcoal, 82. 
Pyrometers, absolute zero in, 275. 

— air, Regnault's, 278. 

— Baird and Tatlock, 293. 

— Baly and Chorley, 277. 

— Barus (Dr. Carl) on bases for, 272. 

— based on expansion of solids, 273. 
liquids, 274. 

— Callander's silica bulb, 279. 

— Centigrade or Celsius scale, 270. 

— conditions for good, 271. 

— conduction, 285. 

— constant pressure methods, 279. 
volume methods, 279. 



INDEX 



379 



Pyrometers, Cornu-le-Chatelier, 286, 287. 

— Daniell's, 273. 

— Deville and Troost's iodine, 278. 

— electric, 290. 

— expansion of liquids for, 274. 

— Fahrenheit scale, 270. 

— Fery absorption, 287. 

radiation, 295. 

spiral, 296, 297. 

— fusion, for hot-blast temperatures, 280. 
metals and alloys suitable for, 280. 

— Jourdes', 285. 

— Krupp's, 283, 284. 

— Le Chatelier, 292. 

— linear expansion of solids for, 273. 

— liquid expansion for lower temperatures, 274. 

— Mercury thermometer, 275. 

— Mesure and Noel's, 288. 

— method of mixtures, 282. 

— optical, 285. 

— properties used for, 272. 

— radiation, Fery, 295. 

— recording forms for, 293-295. 

— Regnault's air, 278. 

— Schaffer and Budenberg's, 274. 

— Seger cones, 281. 

— Siemens', 282, 283. 
electric, 290-292. 

— specific heat, 282. 

— Thread recorder for, 293, 294. 

— vapour tension, 272. 

— Wanner, 288-290. 

— Whipple indicator for, 291. 
Pyrometric methods, properties used for, 272. 
Pyrometry, 268-297. 

Quartzites, 330. 

Quigley's results with Rockwell furnace, 259. 

Radiation heating, 20. 

— losses in gas producers, No. 2, 174. 

— of heat from gas producers, 170. 

— pyrometer, Fery's, 295. 
Radiators, bad and good, 20, 21. 

Rankine on rate of combustion in various 
grates, 229. 

Rarer elements in coals, 68. 

Rate of combustion, Rankine's figures, 229. 

fall in water of bodies equal in size, un- 
equal in weight, 119. 

Reaumur thermometer scale, 270. 

Recorders, couples, 294. 

— heating and cooling curves, 294. 

— photographic, 294. 

— ribbon, 294. 

— thread, 293, 294. 
Recording gas calorimeters, 313. 
Recovery of by-products, 193-202. 

from coke-ovens, 193. 

Pierce charcoal process, 80. 

Recovery ovens, enormous annual loss from 

neglect of, in. 
Recuperators. See Regenerators. 
Red charcoal, 75. 
Refinery hearth, 222, 223. 
Refractoriness, 360. 

— of fire-clays, effect of loads on, 360. 
Refractory materials, 329-363. 
classified, 329. 

committee's specifications, 357. 

for fire-bricks, blocks, tiles, etc., 

358. 
retort material, blocks, etc., 

359- 

silica bricks, blocks, etc., 359. 

Regenerative furnaces, Siemens', 143, 242. 



Regenerative furnaces, Siemen's at Wishaw,243> 

other forms, 245. 

Krause's efficiency figures of, 251. 

— gas-kiln at Glenboig, 342-344. 
Regenerators, action of, 243-245. 

— Batho furnace, 246. 

— Gorman's furnace, 249. 

— Otto-Hoffman coke-oven, 103, 104. 

— Ponsard's furnace, 249. 

— position of, 250. 

— Siemens', 242-248. 
new form, 248. 

— Simon-Carves coke-oven, 101-103. 

— Thwaite's Ideal, 249. 
Regnault's air thermometer, 278. 
Reheating furnace, details of, 227. 
Removal of products of combustion, 265. 

smoke, three essential conditions, 265. 

sulphur from coke, 112. 

Resistance pyrometer, Siemens' electric, 290. 
Results, calculated and determined, compared, 

314- 
Results of coal washing, 124. 
Retort coke-ovens, 90. 

Appolt, 96. 

Coppee, 98. 

— furnaces, 235, 236. 

— material, standard specifications for, 357. 
Reverberatory furnaces, 224. 

Cubillo's heat balance of, 230. 

details of some, 227. 

for calcining copper ores, 224. 

rates of combustion in various, 229. 

Rockwell, 258. 

Stetefeldt, 232, 233. 

" Revergen " gas furnace, 256. 

Reversibility, law of, 28. 

Revolving-bottom gas producer, Taylor, 157. 

Ribbon recorders, 294. 

Rittinger formula for rate of fall in water or 

equal-sized bodies of unequal weight, 119. 
Roasters, close, 235. 

Roasting in reverberatory furnaces, 225. 
Robinson's coal- washer, 120. 
Rockwell oil furnace, 258. 

Quigley's experiments with, 259. 

Rosenhain's calorimeter, 303. 

Rothkohle, 75. 

Rumford's calorimeter, 298. 

Russian crude petroleum, analysed, 126. 

Russia's percentage of world coal, 55. 

Salamander crucibles, 355. 

Sand for Siemens' hearths, 347. 

Sandstone, 329. 

Schaffer and Budenberg's pyrometer, 274. 

Scotch blast-furnace gases analysed, 180. 

— iron-ore kiln, 213, 214. 

— ore hearth, 223. 
Scrubbers, tower, 200. 

Seger cones, for high temperatures, 281. 

softening points of, 281. 

Selection of a coal for coke-making, 88. 

materials for crucible making, 350. 

Semet-Solvay coke-oven, 90, 107. 
Shale oils, 130. 

analysed, 130. 

separated from coal, 124. 

Siberia's percentage of world coal, 55. 
Siemens' closed-hearth gas producer, 148. 

— electric pyrometer, 290. 

— Frederick, furnace, 246-248. 

— gas producers, 143-149. 

analysis of gas, 144. 

circular, 148. 

elevated cooling tube, 145 



380 



INDEX 



Siemens' gas producers, improved, 147. 

— " Hackney " port, 247. 

— pyrometer, 282. 
electric, 290. 

Whipple indicator, 291. 

— regenerative furnace, 242, 246. 
at Wishaw, 243. 

view of values, 245. 

combustion products analysed, 247. 

new form of, 247, 248. 

— steam jet, 149, 150. 
Silesian coke stall, 89. 
Silica bricks, 344, 345. 
analysis of, 363. 

blocks, tiles, etc., 359-363. 

manufacture of, 344. 

— in clay, 330. 
ganister, 335. 

Siliceous materials, analysed, 336. 

for bricks, 345. 

Silver ores, Stetefeldt furnace, 233. 
Simon-Carves coke-oven, 101, 102. 
Simplex gas producer, Thwaite's, 152. 
Skittle pot, 349. 
Small coal treated by Luhrig's fine coal jig, 123. 

— power gas producer, Thwaite's, 160. 
Smith and Wincott's gas producer, 162. 
Smithells on luminous gas flames, 10. 
Smithy char, 96. 

Smoke, abatement of, and coalite, 204. 

— cause of, 19. 

— domestic fire, 19. 

— prevention of, 267. 

— ■ solid material carried off by, 266. 

— what it is, 265. 

— what it is due to, 265. 

Smokeless combustion, three essential con- 
ditions to, 265. 

Smokeless fuel, advantages claimed for, 211. 

attempts at, 202-212. 

Author on chief cause of smoke, 202. 

Author's remedy, 211. 

Barnsley Carbonization Co.'s system, 

208. 

Becker and Serle's attempt and patent, 

205. 

Carbocoal (Smith's) process, 209. 

Chiswick (Del Monte) system, 210. 

coalite process, 204. 

Earl of Dundonald's patent attempt at, 

205. 

M'Laurin's process, 209. 

Merz and M'Lellan, Michie and Week's 

process, 210. 

Parker's coalite patent, 205. 

Premier Tarless Fuel process, 205-208. 

Pringle and Richard's system, 210. 

Summers process, 209. 

Swinburne's proposal, 210. 

three conditions of Author for realiza- 
tion, 265. 

Smokeless steam coals, 61. 

Sodium and potassium, Baly and Chorley's 
thermometer of, 277. 

Soft coke, 83. 

Solid-bottom gas producers, 153. 

Solid fuels, calorific power of, 33. 

Solid prepared fuels, 73-118. 

Solids, expansion of, 273. 

Soot, analyses of, 267. 

— not pure carbon, 9. 

— sulphur in, 267. 

Sources of loss in Beehive coke ovens, 95, 96. 
Specific gravity of coal, how to find, 325. 

coke, 83, 326. 

liquid fuels, 327. 



Specific gravity of peat. See rather, Density 
of peat. 

wood, 45. 

excluding air spaces, 45. 

— heat of gaseous substances, 366. 
Spent tan, straw, etc., fuel use for, 46. 
Spiral pyrometer, Fery, 296. 

Splint coals, 59. 

Spontaneous ignition of coal, 68, 69. 

Sprinkling stokers, 237-240. 

Proctor's, 239, 240. 

Stalls, coke-making in, 89. 
Stannington fire-clay analysed, 333. 
Starting gas producers, 168. 
Steam boilers, 316. 

sources of loss of potential energy in, 317. 

tests and results, 317, 318. 

Steam coals, smokeless, 61. 
Steam-engines, 318. 

— amount of fuel used per H.P., 319. 

— consumption of steam in, 319. 

— efficiency of boilers, 319, 320. 
Steam jet in gas producers, 149. 

Siemens', 150. 

Thwaite's, 151, 152. 

Steam jets for furnaces, 257, 258. 

Steam, sources of heat lost on conveyance into, 
3i7. 

— use of, in gas producers, 170. 

Steel, cooling curve of " Eutectoid," 294. 
Steel furnaces, Batho, 246. 

crucible, 233. 

oil-fired, 260, 261. 

Siemens', 242, 245, 248. 

— — Thwaite's Ideal, 248, 249. 
Steel melting, crucibles for, 351. 
Steele-Harvey cruc.ble oil furnace, 259-261. 

J. W. Krause's test figures cf, 260. 

Stetefeldt chloridizing roasting furnace, 232, 

233- 
Stokers, mechanical, 237, 266. 

— sprinkling, 237. 

Proctor's, 239. 

— ■ underfeed, 240. 

Stourbridge fire-clay, analysed, 333. 

Straw as fuel, 46. 

Strength of coke, 84. 

Strong gas producer, 184. 

Structure of charcoal, Dr. Thourer on, 85. 

coal, 52. 

coke, 52. 

Suction gas producers, 165. 
Sulphate of ammonia from coke, in. 
Sulphur as calcium sulphate, 324. 

— from coke, removal of, 112. 

— in coal, 64, 324. 

in three forms, 323. 

coke, 86. 

soot, 267. 

Supply of air to the furnace, 261-265. 
Supporters of combustion, 1, 4. 
Surface combustion furnaces, 255. 

Bone, M'Court, and Wilson's system, 

255- 

muffle, 256. 

Sweating stage in charcoal burning, 77. 
Swedish meilers for charcoal burning, 81. 

Tables of calorific powers, 72, 367. 

melting and boiling points, 293. 

points by seger cones, 281. 

Tar, 195. 

— analysis of, 198. 

— commercial products of, 198. 

— dehydration, 198. 

— destruction of, in gas producers, 147. 



INDEX 



381 



Tar emulsion, worst cases of, 197. 

— extraction from producer-gas, 197. 

— extractors, 197. 

— ultimate purified products of, 199. 

— yield from carbonization of coal, 195. 
coals, 195. 

cannel, 196. 

Yorkshire, 196. 

coke-oven gases, 193. 

horizontal retorts, 196. 

vertical retorts, 195. 

Tarry matters carried away by gases, 195. 

destroyed in Siemens' gas producers, 147. 

Thwaite's Duplex gas producer, 

157. 
Taylor revolving-bottom gas producer, 156. 
Temperature, calorific power at higher, 36. 

— defined, 268. 

Temperature found by Baird and Tatlock's 

pyrometer, 293. 

Baly and Chorley's thermometer, 277- 

Beckmann differential thermometer, 

304- 

Centigrade thermometer, 270. 

conduction pyrometers, 285. 

Cornu-le-Chatelier's pyrometer, 286. 

Darnell's pyrometer, 273. 

Deville and Troost's pyrometer, 278. 

Fahrenheit thermometer, 270. 

Fery absorption pyrometer, 287. 

radiation pyrometer, 295. 

spiral pyrometer, 296. 

fusion pyrometers, 280. 

Krupp's pyrometer, 283. 

Le Chatelier pyrometer, 292. 

Mercury thermometer, 275. 

Mesure and Noel's pyrometer, 288. 

method of mixtures, 282. 

— optical pyrometers, 285. 

Reaumur thermometer, 270. 

Regnault's air thermometer, 278. 

Schaffer and Budenberg's pyrometer, 

274. 

Seger cones, 28 r. 

Siemens' electric pyrometer, 290. 

pyrometer, 282. 

Wanner pyrometer, 288, 289. 

— measurement of, 269. 
hot-aii blast, 280. 

— of Bunsen flame, it. 
combustion, 4. 

ignition of charcoal, 73. 

preparation of charcoal, 73. 

— recorded automatically, 295. 

Testing clay for fire-brick and crucible making, 

356. 
Testing fuels, 322-329. 
Theory of charcoal preparation, 75. 

process of coking coal, 93. 

Therm, 141. 

Thermal efficiency of regenerative furnaces, 

251. 
Thermal unit, British, 26. 
Thermo-chemical notation, 26. 
Thermo-chemistry, 26. 

— conversion formulae, 26. 

— law of reversibility, 28. 

— notation, 26. 

— three laws of, 27-29. 
Thermo-dynamics, 316. 

— two laws of, 316. 
Thermometers, Baly and Chorley's, 277. 

— Beckmann's differential, 304. 

— Centigrade, 270. 

— Fahrenheit, 270. 

— Mercury, 275. 



Thermometers, Reaumur, 270. 

— Regnault's air, 278. 
Thermometric scales, 270. 

— — absolute zero in, 275. 

connecting formulae, appendix, 365. 

Thompson's calorimeter, 299. 

Thomson's, W., oxygen calorimeter, 301, 305,. 

Thourer's theory of charcoal, 85. 

Thread recorders, 293, 294. 

Thwaite annular steam jet, 151. 

Thwaite's efficiency diagrams, 254. 

— gas producers, Duplex, 157. 

Simplex, 152. 

small power, 160. 

— Ideal furnace, 248, 249. 

Tilting crucible furnaces, Morgan's, 234, 

Steele-Harvey, 259. 

Titanic oxide in fire-clay, 335. 

Toluene, 200. 

Torbanite or Torbanehill mineral, 49. 

Tower scrubbers, 200. 

Town gas, furnaces using, 256. 

Treatment of blast-furnace gas, 202. 

Trees, relative fuel value of, 45. 

Trough coal-washing machines, 120. 

Turbines, steam, 319. 

— - — consumption of coal in, 319, 320- 

importance of economizers, 320. 

Tuyeres for blast-furnaces, 217. 

Ultimate analysis, 328. 

Underfeed stokers, 240. 

United States, percentage of world coal, 55.. 

Units of heat, 26. 

British Thermal Unit, 26. 

calorie, 26. 

— Centigrade unit, 26. 

■ — ■ — temperature, 270. 
Utilization of fuel, 315-322. 

Valuation of coals, 70. 

Valves of Siemens' furnace, arrangement of,,. 

245- 
Vanadium in coal, 68. 
Vapour tension pyrometers, 272. 
Velocities of explosion, Dixon on, 17. 
Violence of explosion and rate of ignition, 17.. 
Volatile liquids, calorimeters for very, 314. 
Volume of products of combustion, 25. 

Wanner optical pyrometer, 288. 
Washers, Holmes, 199. 

— Livesey, 199. 

— mechanical dash, 200. 
Water in coal, 64. 

wood, 43. 

Water-bottom gas producers, 159. 
Water-gas analysed, 181. 

— and producer-gas.heating powers compared,. 
186, 187. 

— calorific power of, 186. 

— carburetted, 189. 

— nature of, 186. 

— very poisonous, 189. 
Water-gas producers, 182. 

Dellwik- Fleischer, 184. 

" Economical," 189. 

■ " Humphries and Glasgow " system, 189. 

Kramer and Aarts', 186, 187. 

Loomis, 183. 

Perry, 188.' 

plant at Leeds Forge, 182. 

Strong, 184. 

Water in wood, 43. 

Water-jacket ed blast-furnace, 221, 222. 



382 



INDEX 



Water-oil-gas, analysis of an average, 190. 

— Pintsch process, 190. 
• — yield, 190. 
Weathering of coal, 69. 

Wegener's patent burner for powdered fuel, 

261. 
Weights of oxygen and air for combustion, 

Appendix, 366. 
Welsbach incandescent burner, 8. 
Welsh coke-oven, 94. 
Welter's law, 41. 
Whipple indicator, 291. 
Wild calorimeter, 301. 
Willow wood, analysed, 43. 

relative fuel value of, 45. 

Wilson gas producer, 153. 

— ■ automatic, 155. 

Wishaw, view of Siemens' furnace at, 243. 
Wood, analyses of various trees, 43. 

— as a fuel, 45. 

— ash of, 44. 

— average composition of air-dried, 44. 

— bituminous, 55. 

— cord of, explained, 81 (note). 

— distillation of, 44. 

— natural fuel of man, 42. 

— relative fuel value of various trees, 45. 

— specific gravity of, 45. 



Wood to coal, passage from, 63, 64. 

— water in, 43. 
Woodall-Ducknam retort, 208. 
Woods, fuel values of various, 45. 
Work, conversion of heat into, 316. 
Working the gas producer, 175. 

World's available coal supply, estimated, 54, 

55- 
World's output of petroleum, 126. 

Xylene, 136, 201. 

Yield of charcoal, effect on, of rapid charring, 
79- 

from American kilns, 81. 

American meilers, 81. 

retorts, 81. 

■ Swedish meilers, 81. 

Yorkshire finery hearth, 223. 

Zero, absolute, 275. 

— displacement of, in thermometers, 276. 

— in Centigrade thermometer, 270. 

Fahrenheit thermometer, 270. 

Reaumur thermometer, 270. 

Zinc, furnace for distilling, 236. 

— in coal, 68. 

Zyromski on dolomites, 339. 



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